Beyond Earth Class 6 Notes Science Chapter 12

Class 6 Science Chapter 12 Notes Beyond Earth

This chapter introduces the wonders of outer space. It covers the complete solar system including Sun, planets, satellites, asteroids, etc. Also, in this chapter, we will study human efforts to explore space and space missions and the possibility of life beyond Earth.

Stars and Constellations

Many stars can be seen in the sky at night. Stars can be bright or dim. They shine with their light. Some groups of stars appear to form patterns that are like shapes of familiar things, animals or characters of stories. Before the arrival of modern technology or even before, the invention of the magnetic compass, recognizing stars and their patterns helped people in finding directions at sea or on land. It is still used in emergencies as a backup method. In earlier times, groups of stars forming patterns were called constellations. Currently, the regions of the sky, which include these groups of stars, are defined as constellations. Some constellations are shown in the Figure given below. The stars are joined by imaginary lines for easy identification. An internationally agreed set of constellation boundaries was defined by the International Astronomical Union (IAU) in the early 20th century. The entire sky is divided into 88 regions. These regions of the sky are now officially defined as constellations.

→ The constellation Orion is often represented as a hunter. There are three stars in the middle, which represent the belt of the hunter.

→ It is believed that the hunter Orion is followed by his dog (constellation Canis Major), which is battling a bull (constellation Taurus).

→ Canis Major contains a star called Sirius, which is the brightest star in the night sky.

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→ In Indian astronomy, the term nakshatra is used to denote either a certain star or a group of stars, such as Ardra, a star called Betelgeuse in the Orion constellation.

→ Krittika is a group of stars called Pleiades in the Taurus constellation.

→ Aldebaran, known as Rohini is a star in the constellation Taurus.

→ The Big Dipper and the Little Dipper are two distinct patterns of stars. The Pole Star or Polaris is a part of the Little Dipper.

→ The Big Dipper lies in the constellation Ursa Major while the Little Dipper lies in the constellation Ursa Minor.

→ In India, the Big Dipper is known as Saptarishi, and the Pole star is known as Dhruva Tara as shown in Figure.

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→ The Pole star appears stationary in the North direction, which helps to locate the North direction in the Northern hemisphere. The Pole star is not visible from the southern hemisphere of Earth.

Night Sky Watching

Light pollution, dust, and smoke are reducing the ability to enjoy and study objects in the night sky. The presence of excessive artificial light at night time is referred to as light pollution. The night sky is best viewed from open dark areas at places, where there is less light and air pollution. But not all stars and constellations are visible from all places on Earth and on all nights in a year.

To find out a star or a constellation
Sky mapping apps help to find out when and in which portion of the sky a star or a constellation will be visible from your location. These apps can be downloaded on mobile phones. Sky Map is a very handy app for the identification of stars, constellations, and planets from mobile phones. Stellarium is another such app and its computer version is free for download and has many features.

Preparation for Night Sky Watching

  • Under the guidance of adults, identify a dark open area for night sky watching. This should be away from lights, tall buildings, and trees.
  • Choose the date and time.
  • Choose a moonless night with no clouds, particularly for the Pole star which is not very bright.
  • It may be useful to have access to a mobile app with a sky map or print-out images of the constellations. Also, carry a magnetic compass to find directions and a notebook to note observations.
  • On the particular day and time selected, go to the identified place with an adult, where the night sky watching is to be done.
  • After reaching there, wait for about half an hour for your eyes to get adjusted to the darkness. This will help you to see the night sky better.
  • You may easily identify the Big Dipper, the Pole Star, a bright constellation, and the star Sirius in the night sky.

Some dark sky reserves and parks have been established around the world. Light pollution in the reserves is controlled to preserve dark skies for research. Many Higher Education Institutions all over the country along with museums and planetariums conduct night sky watching activity.

Our Solar System

The Sun
Sun, the closest star to us, produces heat and light and is the main source of energy on the Earth. It is about 100 times bigger than the Earth in diameter. The distance of the Sun from the Earth is about 150 million km. ‘Astronomical unit’ (AU) is a useful unit for expressing distances within the solar system which is approximately the distance between the Sun and the Earth. Proxima Centauri is another star nearest to us after the Sun, which lies at a distance of about 269000 AU.

There are many more objects in the sky moving around the> Sun. The movement of an object around the Sun is called a revolution. The Sun, eight planets, their moons, and many smaller objects including asteroids and comets, together form the solar system. In most ancient civilizations, Suo was given the status of a deity. In India, the Sun is worshipped as Surya. The Sun is responsible for the growth of plants, maintaining climate, seasons, weather, water cycle,’ and winds all of which are important for sustaining life on the Earth.

Planets
Planets are large spherical objects that revolve around the Sun. Our planet Earth takes nearly one year to complete one revolution. The Earth also rotates about its axis while revolving around the Sun. For one full rotation, the Earth takes about 24 hours which is called a day. Like the Earth, other planets revolve around the Sun.

→ The eight planets, in order of their increasing distance from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

→ The inner four planets nearest to the Sun-Mercury, Venus, Earth, and Mars are smaller in size. They have solid surfaces with rocks on them.

→ Venus is commonly called the Morning Star or the Evening Star, even though it is not a star. It is because it shines bright at dawn and dusk.

→ Mars is called the Red Planet because the soil on Mars is reddish. Hence, it appears red.

→ Earth is called the blue planet as a large portion of the Earth’s surface is covered with water and thus, it appears blue from the space.

→ The four outermost planets Jupiter, Saturn, Uranus, and Neptune are mostly made up of gases. These giant gaseous planets have large flat ring-like structures around them which are made of dust particles and rocky material.

→ Some planets can be seen with the naked eyes but they look like shining dots, just like stars. To distinguish between the two, do remember that stars appear to twinkle a lot.

→ A telescope helps us to view many dim objects which are not visible to our naked eyes directly.

Different names of the planets which are visible to the naked eye are listed in the following table.

Actual Name Another Name
Mercury Budha
Venus Shukra
Earth Prithvi
Mars Mangala
Jupiter Brihaspati or Guru
Saturn Shani

Natural Satellites
Objects that move around the planets are called satellites. Moons are natural satellites of planets. The Earth has one Moon, while Mars has two moons. Jupiter, Saturn, Uranus and Neptune have a large number of moons. Earth can be considered a satellite of the Sun. In general, any object that moves around a much larger object can also be called a satellite.

The Moon
Earth’s natural satellite, the Moon, takes about 27 days to complete one revolution around the Earth and it is about 3,84,000 km away from the Earth.There is no atmosphere on the Moon. The Moon is about a quarter the size of the Earth. The Moon’s surface shows circular bowl-like structures called craters. (Scan the QR code to see). Most of these craters have been formed due to the impact of asteroids or rocks from space hitting the Moon’s surface. India has launched three Chandrayaan missions to study the Moon, and a further mission is being planned.

India’s first mission to the Moon, Chandrayaan-1, was launched in 2008 and the second mission, Chandrayaan-2, in 2019. The third mission, Chandrayaan-3, was launched in July 2023 and its Vikram lander carrying the Pragyanrover successfully landed on the Moon on August 23, 2023. With this mission, India became the first country in the world to achieve a landing near the Moon’s South Pole. To mark this success, the Government of India declared August 23 to be celebrated as National Space Day in India.

Asteroids
Asteroids are rocky irregularly shaped objects in the solar system. Many of these asteroids revolve around the Sun in paths that lie between those of Mars and Jupiter. This region is called the asteroid belt. The sizes of asteroids are from 10 m to about 500 km.

Comets
Visitors from the outer regions of the solar system having long tails are called comets. They are made up of dust, gases, rocks, and ice. As a comet approaches close to the Sun, the frozen material in it starts evaporating. This evaporating material forms the tail of the comet. One famous comet is Halley’s Comet which appears every 76 years. Its last appearance was in 1986. In Sanskrit and a few other Indian languages, a comet is called Dhumaketu. Various tribes in India also call it Pucchya-Taro (star with a tail) or Zendya-Taro (star like a flag).

The Milky-Way Galaxy and the Universe

All the stars we see in the night, sky including our solar system are a part of the Milky Way Galaxy or Akasha Ganga. Our galaxy is called the Milky Way because it appears as a milky band of light in the sky when you see it in a really dark area. There are many galaxies in the outer space beyond the Milky Way Galaxy which constitutes the whole universe.
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Indian Astronomical Observatory Hanle, is situated at the highest peak of Digpa-rasta-Ri mountain range in Hanle. This peak has been renamed Mount Saraswati. It has several telescopes. One of them is called the Himalayan Chandra Telescope, which has been named after the Nobel Prize winning scientist Subrahmanyan Chandrashekhar. The area surrounding this observatory was notified as the Hanle Dark Sky Reserve (HDSR) in December 2022.

→ Constellations: A region in which a group of stars appear to form patterns are called constellations.

→ Sun: Sun is the closest star to us that produces heat and light and is the main source of energy on the Earth.

→ Revolution: The movement of an object around the Sun is called revolution.

→ Planets: Planets are large spherical objects that revolve around the Sun.

→ Satellite: Objects that move around the planets are called satellites.

→ Moon: Moons are the natural satellites of planets.

→ Asteroid: Asteroids are rocky irregular-shaped objects in the solar system revolving around the Sun between the paths of Mars and Jupiter.

→ Comet: Visitors from the outer regions of the solar system having long tails are called comets.

→ Solar System: The Sun, eight planets, their moons and many smaller objects including asteroids and comets, together form the solar system.

→ Milky-Way Galaxy is an isolated collection of all the stars we see in the night sky including our solar system.

Class 6 Science Notes

Nature’s Treasures Class 6 Notes Science Chapter 11

Class 6 Science Chapter 11 Notes Nature’s Treasures

Nature’s treasures refer to the resources provided by the natural environment that are essential for our survival and for making our lives comfortable. Nature’s treasures include air, water, energy from the Sun, soil, rocks, minerals, forests, and fossil fuels. Without these treasures of nature, any form of life on Earth is not possible.

Air

Air is nature’s treasure as it is essential for all living beings for their survival. The air which we breathe in has oxygen, which our bodies need to perform its functions and to live. Without air, plants and animals would not survive and we can survive without food or water for a few days, but we cannot survive without oxygen for even a few minutes. Air, which surrounds the Earth is not made up of a single gas but a mixture of many gases. Air mainly contains nitrogen (78%) and oxygen (21%). Together nitrogen and oxygen make up about 99% of the air. The remaining part (1%) of air consists of argon, carbon dioxide, and other gases in small quantities. The composition of air can be represented with the help of the diagram as shown.
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Percentage, denoted by % is the number of parts in 100 like 21% oxygen in air means from the total of 100 parts of air, 21 parts contain oxygen gas. The composition of air is not the same everywhere. The higher mountain regions contain less oxygen levels than the plain regions. The air in industrial and urban areas has higher levels of carbon dioxide, smoke, and dust than the air in villages.

Wind
Moving air is known as wind. Wind helps to cool us down on hot days and is used to generate electricity in windmills. When the wind blows, it rotates the wings of a windmill. Windmills can be used to run flour mills (grind wheat into flour), and pull water up from a well. In India, there are many windmill farms, which are areas that have a large number of windmills. These farms use the energy of the wind to generate electricity, which helps to power homes and industries.
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Kutch Wind Farm, in Gujarat, is one of the largest wind farms in India. Other windmill farms in India are Jaisalmer Wind Park in Rajasthan, Muppandal Wind Farm in Tamil Nadu, Brahmanvel Wind Farm in Maharashtra, etc.

Water

Water is one of nature’s most precious treasures because it is essential for all life on Earth. Water is found abundantly on the Earth, as about two-thirds of the total earth’s surface is covered with water. Most of the water is found in the oceans and seas and is saline or salty. Saline water is not directly usable, as it contains a large amount of salt, which is not fit for drinking, domestic, agricultural, and industrial use. Only a small amount of water on Earth is suitable for all these activities, which is called freshwater. It is present in rivers, lakes, ponds, ice sheets, snow, and groundwater. We need fresh water for drinking and many other activities, like cleaning, washing clothes and utensils etc. Freshwater present in ice sheets, snow, and underground water is difficult to access for doing these activities whereas, freshwater present in rivers, lakes, wells, and ponds is easy to access.
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Responsibilities Towards Water
“Water is our responsibility before it is our right”. Even though we all have the right to use water, we must also take responsibility for it. This means we need to be careful not to waste water and to keep our water sources clean. If we waste water or pollute it, we might not have enough clean water for ourselves and others in the future. So, it is our job to use water wisely and to save it. Water gets polluted by human activities, which makes it unsafe for consumption by living beings. Some activities that lead to water pollution are

  • Wastes from homes and industries are dumped into the water.
  • Harmful chemicals from factories are sometimes dumped into rivers and lakes.
  • Harmful chemicals containing fertilizers and pesticides used in farming can come into water bodies during rain.
  • Throwing plastic and other garbage into rivers or lakes.

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So, to reduce water pollution, we can dispose of chemicals properly, reduce plastic use, choose fertilizers that are safer for the environment, and restrict the throwing of garbage and plastics in the water bodies like rivers, lakes, etc. Also, water can easily be wasted through activities like leaving the tap running, over-watering plants, or using water carelessly. So, there is a need to conserve water as freshwater sources are limited and there is a shortage of water in many parts of India. We should conserve water and use it judiciously, by fixing leaks, turning off the taps when not in use, recycling water, and water harvesting.

Rain Water Harvesting
Water harvesting is a smart way to conserve water. In many homes, schools, and office buildings, rainwater is collected and stored in large quantities, which can be used later on for household chores, watering plants, etc. This method of conserving water is called rainwater harvesting.
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In India, traditional water harvesting methods have been used for centuries. For example, in Rajasthan, people use stepwells, also known as Bawadi, and in Gujarat, they are called Vav. These are special wells with steps leading down to the water, making it easier to access. They are designed to collect and store rainwater as well as water that seeps in from nearby lakes, ponds, and rivers. The walls of these wells are lined with stones, allowing water to seep through and fill the well.
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World Water Day is celebrated on March 22nd every year to remind us how important water is for our lives and our planet. It helps us understand that many people around the world do not have enough clean water to drink and use. World Water Day encourages people to find new ideas and solutions to solve water problems, like finding ways to clean polluted water or using water more wisely.

Energy from the Sun

The Sun is considered one of nature’s treasures because it is the main source of energy, that supports all life on Earth. The Sun provides heat and light, which are used by the plants to make food and grow. This in turn provides food and oxygen for animals and humans, as they eat plants for survival. It also helps in drying of clothes, warming up our homes in winter, brightening up our rooms during the day (so we don’t need to use electric lights), etc. The Sun also plays an important role in the water cycle thus, influences rainfall patterns. Without the Sun, our planet would be a cold, dark place where life could not survive.

In many households in India, water is offered to the Sun early in the morning as an expression of gratitude. Sunlight or solar energy is used to generate energy through solar panels. Solar panels are special devices that capture sunlight and convert it into electricity. This electricity can then be used to power homes, schools and offices. The Sun’s energy can be directly used for cooking in a solar cooker or for heating water in a solar water heater.
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Forests

Forests are large areas covered with dense growth of trees, shrubs, and herbs. Forests play a crucial role in our environment.

  • They produce oxygen, which is essential for humans and animals to breathe.
  • Many products that we use in daily life like paper, wooden tables and chairs, etc., are also obtained from forests.
  • Forests are a natural home for many species of plants and animals including, birds and insects and they provide food and shelter for them.
  • Because of these uses, forests are considered a precious resource that needs to be protected and preserved.

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Unfortunately over the years, forests have been cut down on a large scale, this process is known as deforestation. This loss of forests has serious consequences like loss of habitat for many species, which can result in the disappearance (extinction) of plants and animals.

The loss of forests can also disrupt the water cycle, leading to reduced rainfall and water shortages in some areas. Some ways to protect and preserve the forests are

  • Reducing Deforestation: Follow practices that reduce the cutting down of trees. This includes using paper and wood products wisely.
  • Reforestation: Planting new trees in areas where forests have been cut down which helps to restore lost forests.
  • Spreading Awareness: Spread awareness about the importance of forests and encourage others to take action to protect them.

Van Mahotsav, which means “Tree Planting Festival,” is celebrated in India every year during the first week of July. This special week is dedicated to planting trees and plants and raising awareness about the importance of forests.

Chipko Movement was a special effort in India that started in the early 1970s to save trees and protect forests. In this movement, people, especially women, hugged trees to prevent them from being cut down. They formed human chains around the trees and refused to let go, showing how much they cared about the forests. Their brave actions helped stop the destruction of many trees and raised awareness about the importance of protecting forests for our environment. This movement showed how people can come together to make a big difference in preserving nature.
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Soil, Rocks and Minerals

Forests have a variety of soils. Soil is called nature’s treasure because it is important for supporting biodiversity. It supports the growth of plants and supplies them with nutrients and water, which are essential for food production. It is also home to many tiny organisms, such as worms and insects. Decomposed and decayed plants and animals also become part of the soil.

Soils of different places may be of various colors, because these soils may contain different materials. It can be of different types, some soils can be good for growing crops, while some are good for making bricks. Soil forms through a process that takes thousands of years. It starts with the disintegration (breaking apart) of rocks into smaller particles by using the energy from the Sun, water, and living organisms. Rocks are naturally occurring solids composed of one or more minerals.
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Uses of Soil, Rocks and Minerals
Some of the uses of rocks are the construction of houses, roads, temples, buildings, etc. Some rocks like granite and marble are popular for making durable and attractive table tops and floors, while limestone and sandstone are used in building walls and roads. Some rocks, like slate, are used for roofing, and laterite is used in making bricks. Rocks can also be used in making tools like hand axes and arrowheads.
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The formation of rocks takes thousands to millions of years, so it is important for us to conserve the rocks and use them judiciously. Minerals are the building blocks of rocks and have distinct properties such as hardness, color, and shine. Important metals such as gold, silver, aluminium, copper, iron, etc., are extracted from minerals.

Minerals have a wide range of uses:

  • Minerals like copper, silver, cobalt, and gold are essential in making electronic devices like phones and computers.
  • Minerals like aluminium, iron, etc., are used in the making of airplanes and cars.
  • Precious minerals like diamonds, gold, and silver are used to create beautiful and valuable jewelry.

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Fossil Fuels

Fossil fuels are natural energy sources formed from the remains of plants and microorganisms buried deep inside the Earth, millions of years ago. They include coal, petrol, diesel, kerosene, and natural gas. Petrol, diesel, and kerosene are obtained from petroleum. These fossil fuels are used to generate electricity and they can also be used as a fuel for vehicles. Natural gas is a colorless gas, which is used in cooking and generating electricity. It is nowadays used in the form of Compressed Natural Gas (CNG) which is a cleaner fuel for vehicles, than petrol or diesel as on burning it produces less harmful substances and carbon dioxide, which causes global warming. Also, natural gas and Liquefied Petroleum Gas (LPG) have replaced the use of coal, wood, and cow dung as fuels for cooking in households. Fossil fuels such as coal, petroleum, and natural gas, are available in limited quantities and we will run out of them if we keep using them in the manner that we currently do, as it takes, millions of years for their formation.
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Pollution Due to Fossil Fuels
Fossil fuels when burnt, produce smoke and carbon dioxide (CO2) gas, which significantly pollutes the air and the released carbon dioxide is a major greenhouse gas, which causes global warming. The overuse of fossil fuels has led to serious air pollution problems. For example, cars, buses, and trucks that run on petrol or diesel emit pollutants. Similarly, burning coal for domestic use also releases pollutants into the air. This pollution can have harmful effects on health causing respiratory problems like asthma and bronchitis. It can also contribute to global warming leading to climate change and extreme weather conditions. Reducing our dependence on fossil fuels and finding alternative energy sources is essential for improving air £ quality and protecting both human and environmental health.

Natural Resources: Renewable and Non-renewable

Resources are the substances that fulfill our needs and are essential to sustain our lives. Resources can be classified into two main types, natural resources and man-made resources.

  • The resources which we get from nature are called natural resources.
    Examples of natural resources are air, water, minerals, sunlight, forests, soil, rocks, fossil fuels, etc.
  • The resources that are created by human beings are called human-made (man-made) resources.
    For example, plastic, cars, roads, machines, electric bulbs, solar panels, etc.

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Natural resources are again classified into two categories based on their availability in nature.

Renewable Natural Resources:
The resources that get renewed, replenished, or restored within a reasonable period of time are known as renewable natural resources. These are also known as inexhaustible natural resources. Examples of renewable natural resources are water, air, sunlight, etc.

Non-Renewable Natural Resources:
The resources that are found in nature in limited amounts and once used, get exhausted are called non-renewable resources. They are not produced or replenished within a short period. They are also called exhaustible natural resources. Examples of non-renewable natural resources are coal, natural gas, petroleum, minerals, soil, rocks, etc.

Conservation of Natural Resources

Conservation and responsible use of natural resources are essential to ensure their availability for future generations. Natural resources like water, fossil fuels, and forests, are limited and essential for our consumption and survival. By conserving these resources, we help to preserve the environment and ensure that they will be available for future generations. The practices we can follow to conserve natural resources are

  • Recycling and reducing waste
  • Planting trees
  • Use of fossil fuels should be minimized as it is a non-renewable natural resource and burning of these fossil fuels causes air pollution and impacts global warming.
  • Alternative energy sources, like solar energy, wind energy, etc., should be used instead, as they are renewable resources.
  • “Earth provides enough to satisfy every man’s need but not for every man’s greed.” – M. K. Gandhi

→ Air: It is a mixture of many gases mainly nitrogen (78%) and oxygen (21%).

→ Rainwater Harvesting: The process in which rain water is collected and stored in large quantities, which can be used later on for household chores, watering plants, etc.

→ Forests: Large areas covered with a dense growth of trees, shrubs, and herbs.

→ Rocks: Naturally occurring solids composed of one or more minerals.

→ Minerals: Naturally occurring inorganic substances with a specific chemical composition and structure.

→ Fossil Fuels: Natural energy sources formed from the remains of plants and microorganisms buried deep inside the Earth, millions of years ago.

→ Resources: The substances that are valuable and useful to humans.

→ Natural Resources: The resources which we get from nature.

→ Human-made Resources: The resources that are created by human beings.

→ Renewable Natural Resources: The resources that get renewed, replenished or restored after use within a reasonable period.

→ Non-renewable Natural Resources: The resources that are found in nature in limited amounts and once used, they get exhausted. They are not produced or replenished within a short period.

Class 6 Science Notes

Living Creatures: Exploring their Characteristics Class 6 Notes Science Chapter 10

Class 6 Science Chapter 10 Notes Living Creatures: Exploring their Characteristics

There are numerous entities around us that can be categorized as living or non-living. For instance, dogs, plants, people, birds, and snails are living, while fans and windows are non-living. The distinction between these two categories is based on specific characteristics that define their nature. Understanding these differences helps us to appreciate the diverse nature of our world.

Characteristics of Living Organisms

All living things share certain unique characteristics that set them apart from non-living things. These features not only distinguish them but also highlight the processes that are essential for life. Some of the features of living organisms are as follows.

  • They need food, water, and air to survive.
  • They can grow.
  • They can move on their own.
  • They respond to stimuli.
  • They reproduce themselves.
  • They respire and utilize energy from food.
  • They excrete and get rid of waste materials from their body.
  • They have a definite lifespan.
  • They are made up of living cells.

Non-living things do not perform any of the above functions.

Let us discuss a few important characteristics of living beings in detail.

1. Growth
All living things (plants and animals) show growth by increase in size and weight. When living things grow, they become taller and bigger on their own. For example,

  • A baby grows into an adult.
  • A small puppy grows and becomes a dog.
  • A chicken hatched from an egg grows and becomes a hen or a cock.
  • Similarly, a small plant grows and becomes a big tree.

2. Movement
It is one of the most important signs of life in an organism. All living things move by themselves. Animals can move from one place to another.
Plants are generally anchored in soil so they do not move from one place to another. Instead, they exhibit movement by moving their body parts. For example,

  • Opening of petals in a flower.
  • Winding of climbers around any object placed close to them.
  • Eating of insects by insectivorous plants, such as Drosera, by showing movement in their leaves. Drosera relies on insects for its nutrition. It has saucer-shaped leaves with many hair-like projections of unequal length having sticky ends. Whenever an insect enters the saucer, the hairs move inward and trap the insect with the help of their sticky ends.

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3. Food
All living beings need food (nutrition) for their growth and development. Plants make their own food with the help of sunlight, air, and water, through the process known as photosynthesis. Whereas, animals and humans depend on plants, other animals, and their products for their survival.

4. Respiration
It is a vital process carried out by all living organisms. It is through respiration that the body finally obtains energy from the food it takes. Breathing is a part of respiration. When we inhale, the air moves from the outside to the inside of the body. When we breathe out, we expel the air which was inhaled. This process can also be observed in other animals, such as dogs, cats, cows, and buffaloes, through the movement of their abdomen while they are at rest. All living organisms breathe in oxygen, which is used by their body and gives out carbon dioxide produced in the process. The mechanism for the exchange of gases is different in different organisms. Some examples are given below.

  • Fishes use gills to obtain dissolved oxygen from water.
  • Plants also exchange gases through tiny pores present on the surface of leaves called stomata.

5. Excretion
The process of removal of waste from the body is called excretion. All living things take food, but not all food that is eaten is used. A part of it, which is not used is removed as a waste. Our body also produces waste products during various life processes. These waste products are harmful to our body and need to be removed. Thus, excretion becomes a necessary process that is carried out by all living organisms. In animals, excess water and salts are removed from the body in the form of sweat and urine. Similarly, plants, such as grasses and roses, excrete excess water and minerals in the form of small droplets on their leaves.
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Some plant removes waste through secretions such as gums and resins, which are used as adhesives and for making varnishes, respectively.

6. Response to Stimuli
All living things respond to changes around them. The changes in our surroundings that make us respond to them are called stimuli. A few examples are given below.

  • On touching a hot plate, our hand withdraws suddenly from its surface to avoid burning.
  • We close our eyes, when a sudden bright light is flashed or when we suddenly move from a dark place to bright sunlight.
  • Shoots of plants grow upward and exhibit movement toward sunlight, while roots grow downward in response to gravity.
  • In some plants like Mimosa, commonly known as ‘touch-me-not’ chhui-mui, or lajjalu leaves close or fold when someone touches them.
  • Similarly, the sleeping leaves of the gooseberry (amla) tree that are facing each other tend to come together after sunset.

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Jagadish Chandra Bose (1858-1937) was an Indian scientist, who is known for his interesting experiments with plants. He built a machine called a crescograph to record how plants respond to stimuli like light, heat, electricity, and gravity. This machine, allowed him to measure how fast plants grow. He also showed that plants can sense and respond to stimuli.

7. Reproduction
It is the process by which living things produce more of their kind. It is necessary for the continuity of life. Reproduction takes place in many different ways in different organisms. Some modes of reproduction are given below.

  • Animals like insects, fishes, and birds lay eggs and when these eggs hatch, the young ones come out and grow into adults.
  • Some animals like cats, dogs, cows, and human beings give birth to their young ones.
  • Plants also reproduce. Many plants produce seeds which can germinate and grow into new plants.

When a living being is not able to exhibit all of the above-mentioned characteristics, despite the availability of all resources (like food, air, and water) needed for being alive, it is said to be dead.

Some Exceptions of Living Characteristics
We can conclude that living things may have all the characteristics that we have discussed, while non-living things may not show all these characteristics at the same time.

  • Non-living things like cars, bicycles, clocks, and water in the river move. The moon moves in the sky and a cloud grows in size.
  • Sometimes living things may also not show all the characteristics of the living. For example, seeds stay in a shop for months and do not show any growth or some of the other signs of life. However, when we bring the same seed, plant it in the soil, and water it, it begins to sprout and grow into a whole plant.

Germination of a Seed

In this process, a seed takes in water and starts to swell. As it absorbs moisture, it activates the growth inside the seed. The first thing that happens is the development of roots that grow downward into the soil. At the same time, a shoot begins to grow upward, which will eventually develop into the stem and leaves of the new plant. This growth allows the seed to become a seedling and ultimately a fully-grown plant.

Essential Conditions for Seed Germination
The germination of seeds marks the beginning of a plant’s life cycle and depends on the right amount of water and air. These conditions work together and aid in seed germination in the following ways.

  • Water: It enables the seed to carry out the processes necessary for its growth. Water softens the outer covering of the seed called the seed coat and helps the tiny embryo inside it to develop into a plant.
  • Air: Seeds use the air available in the spaces between soil particles. Moreover, spaces between the soil particles allow roots to grow easily.

Living Creatures Exploring their Characteristics Class 6 Notes Science Chapter 10 4

Most seeds do not need light for germination. However, once germination is complete, sunlight becomes necessary for the seedlings to continue their growth and development. Some flowering plant seeds, such as Coleus and Petunia, need light to germinate. Covering these seeds with soil can prevent them from sprouting. In contrast, seeds of flowering plants like Calendula and Zinnia require darkness to germinate and should be covered with an appropriate amount of soil.

Life Cycle of a Plant

The life cycle of a plant outlines its various stages of development. This process begins with a seed growing into a young plant. As the plant matures, it produces flowers and fruits. The fruit contains seeds that give rise to a new generation of plants. The entire process, from a seed to a plant and then, to the next generation of seeds is called the life cycle of a plant. For a better understanding, the life cycle of a bean plant is illustrated below.
Living Creatures Exploring their Characteristics Class 6 Notes Science Chapter 10 5
When a plant stops growing and all activities of life gradually come to an end, even after the availably of all the necessary conditions, the plant is considered dead.

Life Cycle of Animals

Just like plants, animals also undergo many changes throughout their life cycle. These changes can be quite different depending on the type of animal. The life cycles of the mosquitoes and frogs are discussed below.

Life Cycle of a Mosquito
Mosquitoes are small, flying insects often found near stagnant water sources. They undergo four stages in their life cycle, which are described below.

  • Stage 1 (Egg): The female mosquito lays eggs on or near water, which then hatch into larvae.
  • Stage 2 (Larva): It develops from the eggs and grows into pupae.
  • Stage 3 (Pupa): The pupae transform and eventually become adult mosquitoes.
  • Stage 4 (Adult): The adult mosquitoes that emerge from the pupa rest briefly on the water’s surface and then fly away. They typically live for 10 to 15 days.

Living Creatures Exploring their Characteristics Class 6 Notes Science Chapter 10 6
Throughout these stages, the mosquito undergoes significant changes in appearance, body shape, and structure. The shape of the egg differs greatly from that of the larva; the larva looks distinct from the pupa and the pupa is markedly different from the adult mosquito.

How to Stop Mosquitoes from Breeding?
Female mosquitoes are bloodsucking insects that transmit diseases such as malaria, dengue, and chikungunya to humans. Therefore, it is important to prevent their breeding. This can be done by eliminating common places, where water is likely to stagnate, as the larval and pupal stages of mosquitoes require water for their development. Another method to prevent mosquito breeding is to spray kerosene oil on stagnant water. The oil forms a thin layer on the surface of water separating it from the air. This prevents larvae and pupae from getting air, when they move to the surface to breathe, ultimately causing their death.

The silk moth also goes through four life stages: egg, larva, pupa, and adult. Eggs hatch into larvae, which then grow in size. The larvae produce thread-like material that they wrap around themselves to form a cocoon before transitioning into pupae. These fibers are used to make silk fabric. In India, the Khadi and Village Industries Commission (KVIC) has established several centers for silk production.

Life Cycle of a Frog
Frogs are amphibians that are commonly found near small water bodies and are particularly abundant during the rainy season. They undergo four stages which are described below.

  • Stage 1 (Spawn): An adult frog lays a cluster of jelly-like eggs called spawn on the surface of the water, usually near the edge of a pond. The eggs develop into embryos, which then transform into tadpoles.
  • Stage 2 (Tadpole): In the early tadpole stage, they are characterized by having a tail and no legs, which aids their swimming in the water. As they advance to the later stage, they begin to develop hind legs.
  • Stage 3 (Froglet): In this stage, they still live in water but begin to spend some time on the land. Eventually, they lose their tails and their legs become strong, allowing them to jump on land effectively.
  • Stage 4 (Adult Frog): In this stage, froglets mature into fully developed adult frogs, capable of living both in water and on land.

Living Creatures Exploring their Characteristics Class 6 Notes Science Chapter 10 7
The transformation of a larva into an adult, involving a series of sudden and continuous changes in the body or an animal during its life cycle, is called metamorphosis.

→ Breathing: Process in which air moves in and out of the body.

→ Death: It is the end of life.

→ Excretion: Removal of waste products from the body.

→ Froglet: Stage in the cycle of frogs marked by eventual loss of their tail.

→ Germination: The process by which a plant grows from a seed into a seedling.

→ Growth: The process of increase in size.

→ Larva: It is an early stage in the life cycle of some animals, such as insects.

→ Life Cycle: The series of stages an organism goes through from birth to reproduction and eventually to death.

→ Living: Organisms that interact with their environment to sustain themselves.

→ Movement: The process of changing the position of a body part or the whole body from one place to another.

→ Non-living: Things that do not have life.

→ Nutrition: The process of obtaining and using food to support growth, maintenance, and overall health.

→ Pupa: The life stage in the development of some insects that occurs between the larval and adult stages.

→ Reproduction: The process of producing new ones of its kind.

→ Respiration: The process by which living organisms take in oxygen and release carbon dioxide to release energy.

→ Response: A reaction to a question, experience, or some other type of stimulus.

→ Stimulus: Anything or any event that prompts living beings to respond.

→ Tadpole: The aquatic stage in the life cycle of a frog.

Class 6 Science Notes

Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9

Class 6 Science Chapter 9 Notes Methods of Separation in Everyday Life

Pure Substances and Impure Substances or Mixtures

Pure Substances:
Substances that contain only one type of particle are called pure substances.
For example, sugar, salt, etc.

Mixtures or Impure Substances:
Substances made up of two or more pure substances called components are mixtures or impure substances. All the components of the mixture should retain their original properties in the mixture. Examples of mixtures are air, seawater, soil, tea, milk, coffee, petroleum, etc. Mixtures are classified into two types based on their composition.

  • Homogeneous mixtures have a uniform or the same composition throughout the mixture (it looks the same everywhere).
    Examples include seawater, sugar solution, etc.
  • Heterogeneous mixtures: They do not have a uniform or same composition throughout the mixture (do not look the same everywhere).
    For example, soil, tea, etc.

Why do we need to separate different components from a mixture?
The constituents of a mixture are segregated from each other by the process called separation. For example, grain is separated from stalks, tea leaves are separated from the liquid with a strainer while preparing tea, milk, or curd is churned to separate the butter. Most substances that occur in nature may contain one or more useful substances or one useful substance and one or more harmful or unwanted (undesirable) substances. To make the available substance fit for use, these impurities must be separated from the useful substance. The substances to be separated may be particles of different sizes or materials. These may be solids, liquids or even gases. The separation of substances is carried out for the following purposes.

(i) To remove impurities or harmful compbnents:
Separation helps us to remove harmful substances from the mixture.
For example, small pieces of stones and undesirable seed grains are removed from rice and pulses before cooking. The useless pieces of stones and seed grains are thrown away.

(ii) To remove non-useful components:
Mixtures often contain non-useful substances that need to be separated from the mixture.
For example, tea leaves are separated from the liquid tea with a strainer after preparing tea or before taking it.

(iii) To separate different useful and pure components from mixture:
A mixture may contain one or more useful constituents. These pure components should be separated for their proper use.
For example, when we churn milk, we separate the cream from, the milk to obtain butter, which is used in cooking and baking. Also, we get pure salt from seawater by evaporating the water, leaving only the salt behind.

Methods of Separation of Mixtures

Separation of useful substances from unwanted substances is very common in our day-to-day lives and laboratories/industries. In day-to-day life, we use simple methods to carry out separation. Some most commonly used methods for separating the constituents from a mixture are discussed below.
Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 1

Handpicking
The process of separating solid particles from a mixture by hand is called handpicking. This method is one of the simplest ways to separate substances from a mixture based on their physical properties, particularly when the components have noticeable differences in appearance (size, shape, or color). This method is used when highly larger-sized particles are present in small quantities (impurities) like stone, husk, pieces of dirt, etc. from the grains of wheat, etc. In our everyday lives, we use the method of handpicking to separate stones, husks, which are not useful, from food grains like wheat, rice, and pulses.
Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 2

Threshing
The process of separating grains from stalks of harvested crops is called threshing. Fully matured crops like paddy (rice) or wheat is harvested from the field. During this, the crop plants are cut close to the ground. Stalks are dried in the sun before the grains are separated. Each stalk has many grains attached to it. The grains attached to the stalks are covered in a thin layer called chaff. The grains are then separated from stalks by the process of threshing. In this process, the stalks are beaten to free the grain seeds. Threshing is essential in agriculture to separate grains efficiently from harvested crops like wheat, rice, barley, and oats. Threshing can be done in the following ways.

  • By holding the bundles of stalks in hand and beating them on hard surfaces.
  • By allowing bullocks to trample the stalk.
  • By threshing machines, called threshers, in case of large quantities of grains.

Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 3

Winnowing
The method used to separate heavier and lighter components of a mixture by wind or by blowing air is called winnowing. This method is commonly used by farmers to separate lighter husk particles (thin, dry outer covering of various seeds) from heavier seeds of the grains. The steps involved in the separation of husk from grains with the help of wind are as follows.

  • The mixture of wheat grains and husk is taken in a bamboo winnowing basket (also called chhaaj in Hindi) or plate or newspaper.
  • Farmers take this mixture in an open ground and stand on a risen or elevated platform.
  • The winnowing basket containing the mixture is held at shoulder height then the mixture is allowed to fall by shaking the basket continuously.
  • As a result, lighter husk particles are carried away by the blowing wind. Heavy wheat grains fall straight to the ground and form a heap near the platform for winnowing. The separated husk is used for many purposes such as fodder for cattle.

Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 4
With technological developments, a modern machine thresher has been developed which can be used to perform both the tasks of threshing and winnowing simultaneously.

Sieving
A method used to separate solid particles of different sizes by passing a mixture through a sieve, which is a shallow vessel having holes of the same size at the bottom, is called sieving. The sieves can be of different sizes which depends on the size of the substances to be separated. Some examples of separation of mixtures by sieving are as follows.

  • Sieving allows the fine flour particles to pass through the sieve holes while the bigger impurities (Bran-outer coarse part of the grain) remain on the sieve.
  • On a large scale, such as in a flour mill, impurities like stones and husk are removed from grains before grinding them. Usually, a bag full of wheat grains is poured on a slanting sieve.
  • The sieve removes pieces of stones, stalks, and husk that may still remain with wheat grains after threshing and winnowing.
  • Similar slanting sieves are used at construction sites to separate pebbles and stones from coarse sand.

Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 5
Sieving of wheat flour is not considered a healthy practice because wheat bran which is removed during sieving is a rich source of fibre.

Evaporation
The process of conversion of water into its vapour is called evaporation. Heat and wind help in the evaporation of water. The process of evaporation takes place continuously, wherever water is present. This process is used to obtain a solid material that has dissolved in water or any other liquid. The dissolved substance is left as a solid residue when all the liquid gets evaporated. For example, obtaining salt from seawater. Sea water contains large amounts of salt and some other substances dissolved in it. One of these salts is the common salt. Now, let us understand the way by which it can be obtained.

When seawater is allowed to stand in shallow pits, water gets heated by sunlight and slowly turns into water vapour through evaporation. In a few days, the water evaporates completely leaving behind the solid salts. Common salt is then obtained from these solid salts by further purification. In Ayurveda, the traditional Indian system of holistic health and medicine, herbs or parts of plants are prescribed as remedies. This practice facilitates the evaporation of excess water by drying the ingredients like roots, leaves, flowers, or seeds of various medicinal plants in shade.
Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 6
The process of evaporation takes place at room temperature, but the rate of evaporation increases with the rise in temperature, thus, the evaporation process is faster when the mixture is heated.

Condensation
The process of conversion of water vapour into its liquid form is called condensation. The process of condensation is the opposite of evaporation. In this process, water vapor condenses into a liquid after making contact with the cooled surface. This method is used when the solid and liquid both need to be recovered, e.g. separation of pure water from salt solution.

Sedimentation, Decantation and Filtration
We observed that sometimes, separation of the mixture is not possible with the help of winnowing and handpicking as there may be lighter impurities present such as dust or soil particles. So,, we use other methods for the separation of such a mixture. These methods are as follows.

Sedimentation
The process of settling down of insoluble heavy solid particles in a mixture at the bottom of the vessel is known as sedimentation. For example, when we mix up sand and water in a glass and stir it with a spoon or any other tool and wait for some time, we see that the sand settles down at the bottom and clear water stands on it.
Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 7

Decantation
The process of transfer or separation of clear liquid from one vessel to another vessel without disturbing the sedimented particles is known as decantation. For example, transfer of water to another vessel from a mixture of water and sand.
Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 8
The same principle is used for separating a mixture of two liquids, that do not mix with each other, e.g. oil and water can be separated from their mixture by this process. If a mixture of such liquids, which do not mix with each other, is allowed to stand for some time, they form two separate layers. The component that forms the top layer (i.e. oil) can then be separated by decantation.

Filtration
The process of removing insoluble solid particles from a liquid by using a filter is known as filtration. Filter paper is a commonly used filter, other than this, cotton, charcoal, and sand can also be used as filters. The choice of filter depends upon the size of the particles of the materials to be removed. Some examples of the separation of mixtures by filtration are as follows.

  • Separation of tea leaves from prepared tea by using a strainer.
  • Making tea by using tea bags made up of filter paper. Initially, tea bags were made of soft cloth like silk. It is because it could hold the tea leaves and let hot water pass through. Later, people started using gauze or muslin. Eventually, they began using filter paper.
  • Fruit and vegetable juices are usually filtered before drinking to separate the seeds and solid particles of pulp.
  • In everyday applications, such as purifying drinking water, mud from water, etc.

Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 9
Our kidneys act as a filter to clean the blood. Waste chemicals dissolved in the blood pass through a membrane in the kidneys and are excreted as urine acts or gets filtered.

The filtration method can not be used for the separation of a mixture of two liquids, like milk and water or oil and water. Also, this method only works if the solid component of the mixture is insoluble in the liquid component, thus a mixture of salt in water can not be separated by this method.

Churning
A mechanical process used to separate butter from buttermilk is called churning. It is traditionally significant in households and dairy farms. Churning is done by pouring the buttermilk or curd into a churner (mathni) and rotating the buttermilk or curd vigorously by using a churner. This causes the separation of butter (solid) from the buttermilk or curd. Butter being lighter, floats on the top of liquid buttermilk.
Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 10

Magnetic Separation
A process where magnetic materials are separated from non-magnetic materials, by using a magnet is known as magnetic separation. The magnetic material, like, iron nails is attracted to the magnet and sticks to it, while, the non-magnetic material, like sulphur powder, is not attracted to the magnet.
Methods of Separation in Everyday Life Class 6 Notes Science Chapter 9 11
This method is used in various industries and everyday situations. It is employed in recycling processes to separate magnetic materials (like iron) from the waste materials through a magnet fitted to a crane. This iron is called scrap iron and it can be recycled and reused.

→ Pure Substance: A substance that contains only one type of particle is called a pure substance.

→ Mixture: It is made up of two or more substances, which are called the components of the mixture.

→ Handpicking: It is the method of picking particles from mixtures by hand when the impurities are of slightly large size and in small quantity in the mixture.

→ Chaff: It is the thin, scaly layer that covers the grains attached to the stalks.

→ Threshing: The process of separating grains from stalks of harvested crops.

→ Winnowing: It is the method used to separate heavier and lighter components of a mixture by wind or by blowing air.

→ Sieving: It is a method used to separate solid particles of different sizes by passing a mixture through a sieve.

→ Evaporation: It is a process where a liquid substance is converted into its gaseous state.

→ Condensation: It is the process of conversion of water vapour into its liquid form.

→ Sedimentation: The process of settling down of insoluble heavier solid particles at the bottom of the vessel.

→ Decantation: It is the process of separating the top layer of liquid after sedimentation.

→ Filtration: It is a method used to separate a mixture of an insoluble solid and a liquid by passing it through a filter.

→ Magnetic Separation: It is a process where magnetic materials are separated from non-magnetic materials by using a magnet.

→ Churning: It is a mechanical process used to separate butter from buttermilk.

Class 6 Science Notes

A Journey through States of Water Class 6 Notes Science Chapter 8

Class 6 Science Chapter 8 Notes A Journey through States of Water

Water is one of the most crucial substances on earth. It is fundamental to all forms of life and essential for various natural processes. We need water for drinking and many other activities, like cleaning, washing clothes and utensils, etc. Water is found abundantly on the planet Earth, as about 3/4th of the total earth’s surface is covered with water but only a small amount of this water is suitable for plants, animals, and humans, like water from rivers, lakes, ponds, and groundwater. Most of the water is in the oceans and is not directly usable, as it contains large amounts of salt. Water is unique because it can exist in three distinct states- solid, liquid, and gas, each playing a vital role in our environment.

Different States of Water

As we know water exists in different forms, like ice, water, and water vapour. These forms show different properties and are called states. Different states of water and its properties are
1. Solid State (Ice)

  • Water turns into ice when water is kept in a freezer.
  • Ice has a definite shape and volume. It retains its shape irrespective of the container it is kept in.
  • Ice does not flow or spread.

A Journey through States of Water Class 6 Notes Science Chapter 8 1

2. Liquid State (Water)

  • When ice is heated, it melts into liquid water.
  • Liquid water has a definite volume. It does not have a fixed shape and takes the shape of the container it is kept in.
  • It flows or spreads, and moves freely.

A Journey through States of Water Class 6 Notes Science Chapter 8 2

3. Gaseous State (Water vapour)

  • Heating water turns it into steam or water vapour.
  • The water that evaporates during some processes, like the drying of clothes or mopping of floors contributes to the water vapor present in the air around us.
  • Water vapour fills the entire space available and has neither a fixed shape nor volume.
  • The water vapour spreads out and moved rapidly.

A Journey through States of Water Class 6 Notes Science Chapter 8 3

The water vapour is not visible but it is still present in the air. The tiny droplets of water in the water vapor or steam make it visible.

Changing States of Water

Imagine a piece of ice, a glass of water, and steam coming out from a boiling kettle. They might look different, but they are all made of water. This is because water is a substance that can change its state from solid to liquid and liquid to gas on continuous heating. When ice melts, it turns into water. When water heats up, it becomes steam. And when steam cools down, it turns back into water. The processes involved in changing the state of water are

  • Melting: The process of conversion of solid into liquid on heating is called melting.
  • Freezing: The process of conversion of liquid into solid on cooling is called freezing. Water freezes when cooled below 0°C.
  • Evaporation: The process of conversion of liquid into gas on heating is called evaporation. The process of evaporation of water takes place continuously (without any help) even at room temperature. Drying of wet clothes, mopped floors, and sweat from our bodies are examples of evaporation.
  • Condensation: The process where water vapour turns back into liquid water when cooled is known as condensation.
    A Journey through States of Water Class 6 Notes Science Chapter 8 4

Another example of changing state from solid to liquid is the melting of candle wax. The candle wax which is solid melts into liquid wax, when it is heated. Whereas, the liquid wax on cooling, turns into solid candle wax.

Daily Life Example of Water Condensation

When a glass of cold water is taken out from the refrigerator on a warm day, water droplets form on the surface of the glass. This happens because the warm, moist air around the glass, containing water vapour, cools down upon contact with the cold surface and the water vapour condenses into liquid droplets. Also, condensation is often seen on bathroom mirrors after a hot shower, where warm steam from the shower cools and forms droplets on the cooler surface of the mirror.
A Journey through States of Water Class 6 Notes Science Chapter 8 5
Atmospheric Water Generator (AWG) machines are used to collect water from humid air to produce drinkable water. This is done by cooling the air, which causes condensation of water vapour.

Evaporation: Self-Disappearing Act of Water
You may notice that water levels in a container or a puddle disappear over time. This is due to evaporation, where the water has turned into water vapour. The process of conversion of water into its vapour state is called evaporation.

Rate of Evaporation

The evaporation of water can be faster or slower, depending on several factors, which are as follows.

1. Temperature:
Higher temperatures increase the rate of evaporation. When water is heated, its molecules gain energy, move faster, and escape more easily into the air as vapour. Similarly, lower temperatures slow down the rate of evaporation. Cooler water has less molecular energy, so fewer molecules have enough energy to escape the liquid state.

2. Surface Area:
Evaporation is a surface phenomenon. Increasing the surface area of water exposed to air speeds up evaporation. For example, spreading water out in a steel plate allows more water to be exposed to air as compared to the water filled in the cap of a bottle. Decreasing the surface area, such as using a small container, limits the area available for evaporation and thus slows down the process.

3. Air Movement (Wind):
Increased air movement or wind accelerates evaporation. Moving air carries away the water vapour that has formed above the liquid surface, reducing humidity and allowing more water to evaporate.

4. Humidity:
Humidity is the amount of water vapour present in the air. Lower humidity levels in the air enhance evaporation. When the air is dry, it has a greater capacity to absorb additional water vapour, leading to faster evaporation. High humidity levels mean the air already has more amount of water or has more humidity, so the rate of evaporation decreases because the air can hold less additional water vapour.

Examples showing how these factors influence the rate of evaporation are

  • Drying Clothes: Clothes dry faster on a hot, windy day as compared to a cold and not-so-windy day because higher temperatures and air movement increase the rate of evaporation of water from the clothes. On rainy days, the amount of water vapour in the air is more, therefore, rainy days are more humid. So, it is difficult to dry clothes on rainy days as the rate of evaporation is less due to more humidity.
  • Puddles: A large puddle present in the area getting direct sunlight will evaporate faster than a small puddle present in the shade, due to increased surface area and higher temperature.
  • Drying Dishes: Dishes placed on a dish rack in an area with warm, dry air will dry faster, as the increased air circulation and heat help the water on the dishes to evaporate more quickly.

Cooling Effect of Evaporation

When water evaporates, it needs heat to change into a gas. The heat comes from the things around it (surroundings). As the heat is used up for evaporation, the water and the surface where it was, become cooler and give a cooling effect. Examples showing the cooling effect of evaporation are

(i) When you sweat, your body releases water onto your skin. As the sweat (water) evaporates into the air, it takes heat away from your skin, making you feel cooler.

(ii) On a hot day, the water in a matka (earthen pot) stays cool, so when you drink it, it feels refreshing. Matkas are made up of clay, which has tiny holes. When you fill it with water and leave outside, the water seeps through the surface of the matka and starts to evaporate. As the water evaporates, it makes the water inside the matka cooler than the temperature of the air around it.
A Journey through States of Water Class 6 Notes Science Chapter 8 6
(iii) Similar to matkas, surahis are also made up of clay. They are used to store water and have a similar evaporation and cooling process. The cooling effect helps keep the water inside the surahi cool, which is especially nice to drink in summer days.
A Journey through States of Water Class 6 Notes Science Chapter 8 7

Plants take in water from the soil through their roots. The water travels up through the plant’s stem (or trunk) to the leaves. In the leaves, some of this water evaporates into the air through the stomata. The process by which plants lose water through tiny openings (stomata) in their leaves is called transpiration. Just like how sweating cools you down, transpiration provides a cooling effect to the plant.

Formation of Clouds to Give Rain

As a result of evaporation, water vapour from the earth rises higher above the earth’s surface as water vapour is lighter than air. It cools down and changes into tiny water droplets, which are generally formed around the dust particles. These small droplets float in the air and form clouds. Many droplets join together to form bigger drops of water. Some drops became so heavy that they started falling in the form of rain.

The Water Cycle

The water cycle is the continuous movement of water on, above, and below the surface of the earth. It describes how water changes its form and travels through different stages in nature. Water evaporates from the surface of the earth, rises into the atmosphere, cools down condenses to form clouds, and falls again to the surface as precipitation. This circulation of water is known as the water cycle.
A Journey through States of Water Class 6 Notes Science Chapter 8 8
It is crucial for distributing fresh water across the planet. It supports all forms of life, helps regulate climate, and replenishes groundwater.

→ Melting: The process where solid ice turns into liquid water upon heating.

→ Freezing: The process where liquid water turns into solid ice upon when cooled below 0°C.

→ Evaporation: The process where liquid water turns into a water vapour or steam when heated.

→ Condensation: The process where water vapour turns back into liquid water when cooled.

→ Humidity: The amount of water vapour or moisture present in the air.

→ Water Cycle: The circulation of water between the Earth’s surface and atmosphere.

→ Precipitation: The term used to describe any form of water, like, rain, snow, or hail, that falls on the Earth from the atmosphere.

Class 6 Science Notes

Temperature and its Measurement Class 6 Notes Science Chapter 7

Class 6 Science Chapter 7 Notes Temperature and its Measurement

In this chapter, we will learn about a reliable measure of the hotness or coldness of anybody. We come across various types of thermometers in our day-to-day life. Here, we will develop an understanding of which ones to use where, and how to use them effectively.

Hot or Cold

In our everyday life, we come across various objects, out of which some are felt hot while others can be felt cold. For example

  • A steel bench becomes hot on a bright sunny day but a clay brick remains cold.
  • A cane of cold drink feels cold to touch but touching ice feels colder.

Hence, among these hot or cold objects, some objects may be hotter or colder than the other. So, we can say that the relative hotness or coldness of objects can be decided by simply touching the objects. But our sense of touch is not enough to decide whether the object is hot or cold. A reliable measure of the hotness (or coldness) of a body is its temperature.

Temperature and its Measurement

The degree of hotness or coldness of an object is known as the temperature of the object. A hotter body has a higher temperature than a colder body. A device that measures temperature is called a thermometer. There are two types of thermometers that you are likely to come across

  • Clinical thermometers
  • Laboratory thermometers

Clinical thermometers are used to measure human body temperatures, whereas laboratory thermometers are used for many other purposes.

Different Scales of Temperature
→ The temperature of an object should always be stated with its unit. The most common unit for measuring temperature is degree Celsius (°C). The clinical thermometers generally use the Celsius scale for measuring temperature.

→ There is another scale of temperature known as the Fahrenheit scale. On this scale, the unit of temperature is degree Fahrenheit and is denoted by °F.

→ We can easily convert the temperature from Celsius scale to Kelvin scale by using T(K) = T(°C) + 273.15

→ There is another scale of temperature known as the Kelvin scale. On this scale, the unit for temperature is kelvin and is denoted by K. The SI unit of temperature is kelvin.

→ All three temperature scales Celsius, Fahrenheit, and Kelvin are named in honor of the scientists who developed these scales.

Way of Writing Units
→ The names of temperature scales-Celsius scale, Fahrenheit scale, and Kelvin scale start with a capital letter.

→ The unit kelvin starts with a lowercase letter. The symbols of all units (°C, °F, K) are capital letters. Note that the degree sign (°) is not written with K.

→ While writing the temperature, a space is left between the number and the unit.

→ For temperatures more than one degree, use the plural of ‘degree’, that is, ‘degrees’ while writing the full form of the unit.

Measuring Temperature through Clinical Thermometer

A clinical thermometer is given in the figure below which shows temperatures digitally. It is generally used for measuring our body temperature. These are also known as digital clinical thermometers and run on batteries. Temperature in a digital thermometer is determined with the help of heat sensors.
Temperature and its Measurement Class 6 Notes Science Chapter 7 1

Reading a Digital Clinical Thermometer
→ Wash your hands and the tip of the digital thermometer with an antiseptic solution or clean water.

→ Reset the thermometer by pressing the reset button and placing it under the tongue.

→ Wait till the thermometer makes a beeping sound.

→ Take it out of the mouth and read the temperature on the digital display.

→ Clean the tip of the thermometer again as done before using it.

Precautions to be taken While Using a Digital Clinical Thermometer
→ Use it after reading the instruction manual of the thermometer.

→ Wash the tip of the thermometer with soap and water before and after use.

→ Make sure to keep the digital portion (i.e. display) of the thermometer out of water while washing it.

→ Do not hold the thermometer by the tip.

The normal temperature of a healthy human body is taken to be 37.0 °C, which is equivalent to 98.6 °F on a Fahrenheit scale. However, body temperature is influenced by several factors, such as age, time of the day, and activity level. The temperature of human beings does not normally go below 35 °C or above 42 °C.

In the olden days, before thermometers were developed, fever was detected by checking the pulse rate of a person. However, apart from fever, some other situations also affect the pulse rate. Hence, pulse rate alone is not a reliable indicator of fever.

Mercury Thermometer
Mercury thermometers are also used for measuring the body temperature. But mercury is an extremely toxic substance and is difficult to dispose of if the thermometer breaks accidentally. Digital thermometers pose no such risk and also the numbers in their display are easier to read. Therefore, mercury thermometers are being replaced by digital thermometers.
Temperature and its Measurement Class 6 Notes Science Chapter 7 2
The non-contact thermometers, used during the Covid-19 pandemic, are called infrared thermometers. Such thermometers can measure temperature without touching a person’s body and thus, reduce the risk of spreading disease.

Measuring Temperature through Laboratory Thermometer

A laboratory thermometer consists of a long, narrow, uniform glass tube that is sealed. There is a bulb at one end of the tube which contains a liquid. Outside the bulb in the tube, a narrow column of liquid can be seen. There is a Celsius scale marked along the tube. The liquid column rises or falls with a temperature change.
Temperature and its Measurement Class 6 Notes Science Chapter 7 3

→ The range of a laboratory thermometer is from -10 °C to 110 °C.

→ Before reading a laboratory thermometer, it is very important to find the smallest value that a given laboratory thermometer can read.

→ To find that, divide the temperature difference between two bigger marks by the number of divisions present between them.

→ The temperature reading can be recorded by looking at the mark on the Celsius scale with which the top level of the liquid column coincides.

The correct way of measuring temperature using a laboratory thermometer
→ When the thermometer is immersed in water, its bulb should not touch the bottom or the sides of the beaker.

→ The thermometer should be held vertically as shown in the figure. It should not be tilted.

→ The temperature must be read while the thermometer is immersed in water.
Temperature and its Measurement Class 6 Notes Science Chapter 7 4
→ While reading the thermometer, the eye should be directly in line with the level of the liquid column to be read.

→ The temperature of water remains constant while it is boiling. Also, the temperature of ice remains constant while it is melting.

Precautions to be taken while using a laboratory thermometer
→ Handle with care. If it hits against some hard object, it can break.

→ Do not hold it by the bulb.

→ The liquid used in the laboratory thermometer is generally alcohol or mercury.

Air Temperature

The temperature of air at a particular time is called air temperature. Weather reports shown on TV, newspapers, and the Internet show the maximum and minimum air temperature of the day.

Thermometers that give an approximate idea of the air temperatures are called maximum and minimum thermometers. These can be generally seen on the walls of school laboratories, doctor’s clinics, and hospitals. Weather reports also mention the maximum and minimum air temperature of the day.
Temperature and its Measurement Class 6 Notes Science Chapter 7 5
These temperatures usually vary every day, because weather depends on several factors. There are many techniques for measuring air temperature. The data gathered on air temperature along with various other parameters are used for making weather forecasts. The temperature at the core of the sun reaches as high as 15 million degrees Celsius and there is no limit on the highest temperature that can exist.

Anna Mani (1918-2001) was an Indian scientist, also known as the ‘Weather Woman of India’. She invented and built a large number of weather measurement instruments. This reduced the reliance of India on other nations for such instruments. She also explored the possibilities of using wind and solar energy in India. Her work helped India to become one of the global leaders in renewable energy.
Temperature and its Measurement Class 6 Notes Science Chapter 7 6

Scottish-Irish physicist, William Thomson aka Lord Kelvin is best known today for inventing the international system of a unit of temperature that bears his name, Kelvin. He discovered that in this temperature scale, -273 °C (or 0 K) is considered as absolute zero. He noted that molecules stop moving at absolute zero. It is therefore the lowest possible temperature, or the absolute zero on any temperature scale.
Temperature and its Measurement Class 6 Notes Science Chapter 7 7

→ Temperature: A measure of the degree of hotness or coldness of an object is its temperature.

→ Thermometer: A device that measures temperature is called a thermometer.

→ Clinical thermometer: A thermometer used to measure human body temperature is a clinical thermometer.

→ Laboratory thermometer: A thermometer used to measure temperatures other than human body temperature is a laboratory thermometer.

→ Kelvin: Kelvin is the SI unit of temperature.

→ Celsius Scale: For measuring temperatures, clinical thermometers generally use a scale called the Celsius scale.

→ Degree Celsius: On the Celsius scale, the unit of temperature is degree Celsius and is denoted by °C.

→ Degree Fahrenheit: On the Fahrenheit scale, the unit of temperature is degree Fahrenheit and is denoted by °F.

→ Fahrenheit Scale is a temperature scale that uses the degree Fahrenheit (Symbol: °F).

→ Air temperature: Air temperature is a measure of how hot or cold the air is.

Class 6 Science Notes

Materials Around Us Class 6 Notes Science Chapter 6

Class 6 Science Chapter 6 Notes Materials Around Us

Grouping of Materials

Different objects are made up of different materials. The method of arranging the objects into groups is called classification. The classification is done to group the objects according to the materials they are made up of.

  • The same object can be made up of different materials, e.g. plate can be made up of steel, glass, plastics, etc., similarly, toys can be made up of plastics, rubber, metal, etc.
  • Different types of objects can be made up of the same material, e.g. leather, which can be used to make belts, wallets, purses, bags, etc. Similarly, we can classify materials based on the similarities and differences in their properties.

Different Properties of Materials

We choose materials for making an object based on the properties of materials and the purpose for which the object is to be used. For example, we make a tumbler from materials such as glass, plastic or steel because all these materials have the property of storing water or other liquids. But, we cannot make a tumbler from a piece of cloth because it cannot hold water. Similarly, it would not be a wise idea to use paper for cooking utensils. Now, here is how some of these properties help us pick the right material for each purpose.
Materials Around Us Class 6 Notes Science Chapter 6 1

Appearance
Some materials have a shiny appearance, while some materials might appear dull. For example, gold, silver, and iron appear shiny, while wood, plastic, paper, and rubber have a dull appearance. Materials that appear shiny are said to have luster (or in Hindi chamak) and thus, are called lustrous materials. Such materials with luster are usually metals. However, these metals often lose their shine and become dull when they are exposed to air and moisture. Their shine reappears when they are freshly cut or their surface is scratched.

Non-lustrous materials are those that do not have a shiny surface and have a dull appearance like paper, wood, rubber, chalk, plastic, and jute. It should be noted that not all the materials that shine need to be metals in the same way as all the glitters are not gold. The surface of some materials is made shiny by polishing or creating them with thin layers of plastic, wax, or any other materials that make them look shiny.

Hardness and Softness
Materials that are difficult to compress or scratch are called hard materials. For example, wood, steel, iron, stone, diamond, brick, glass, etc. Materials that can be compressed or scratched easily are called soft materials. For example, sponge, wool, cotton, rubber, butter, chalk, feather, jelly, clay, etc. The properties of hardness and softness are relative. For example, rubber is harder than sponge but softer than wood. Diamond is known as the hardest natural material.
Materials Around Us Class 6 Notes Science Chapter 6 2

Transparency
Based on the property of a material which tells whether we can see through it clearly or not, materials are classified into three types as follows.

(i) Transparent Materials:
Materials through which we can see are called transparent materials.
For example, glass, air, water, alcohol, cellophane paper, etc.

(ii) Translucent Materials:
Materials through which we cannot see are called translucent materials (or semi-transparent materials).
For example, butter paper, frosted glass, oiled paper, clouds, etc.

(iii) Opaque Materials:
Materials through which we cannot see at all are called opaque materials.
For example, cardboard, rocks, bricks, wood, stone, metals, notebooks, etc.
Materials Around Us Class 6 Notes Science Chapter 6 3

Clean water is also a transparent material. This can be understood as when we put any object (say a coin) in a glass filled with clean water, we can see the coin clearly at the bottom of the glass.

Solubility in Water
Solubility is defined as the ability of a solid, liquid, or gaseous substance to dissolve in a solvent (usually liquid). Materials are classified into two types based on solubility.

  • Soluble materials in water: The materials that disappear when mixed in water, i.e. they dissolve in water, are called soluble materials.
  • Insoluble materials in water: The materials that do not disappear when mixed in water, even if we stir them for a long time are called insoluble materials.

Solubility of Solid in Water

  • Some solids completely dissolve or disappear in water and are soluble in water. For example, sugar, salt, milk, lemon juice, alcohol, copper sulphate, baking soda, washing soda, etc.
  • Whereas, some solids do not completely dissolve or disappear in water and are insoluble in water. For example, sand, chalk powder, plastic, paper, wax, oil, petrol, glass, kerosene, wood, etc.
    Materials Around Us Class 6 Notes Science Chapter 6 4

Solubility of Liquid in Water
Some liquids are soluble (miscible) in water as they dissolve in water and do not form a separate layer when mixed with water. For example, milk, lemon juice, glycerine, vinegar, alcohol, etc., whereas, some liquids are not soluble (immiscible) in water as they do not dissolve in water and form a separate layer when mixed with water. For example, petrol, coconut oil, groundnut oil, olive oil, kerosene, etc.
Materials Around Us Class 6 Notes Science Chapter 6 5

Solubility of Gases in Water
Some gases are soluble in water, while some gases are not. For example, oxygen gas dissolves in water and is very important for the survival of animals and plants that live in water. Carbon dioxide gas also dissolves in water and helps in photosynthesis in underwater plants. Some gases like nitrogen and hydrogen are not soluble in water. Water is an important part of our body, it helps in dissolving a large number of materials. The substance in which a material is dissolved is called a solvent and water is known as the universal solvent. The only drawback with water is that it cannot dissolve all the materials.

Mass
Mass is a property that measures how heavier or lighter an object is. It is the amount Of substance that makes up an object. Sometimes, the word weight is used instead of the mass of an object. Weighing balance is used to measure the weight of objects. The units to measure mass are kilogram (kg) and gram (g).
Materials Around Us Class 6 Notes Science Chapter 6 6
When we weigh objects, we observe that some objects are heavier while some are lighter. So, the heavier object is said to have more mass, and the object Weighing a lighter paper cup is said to have less mass.

Space and Volume
Space is the amount of area an object occupies, which can vary depending on its shape and size. The amount of space occupied by a liquid is called its volume. The volume can be measured by using two units litre (L) and millilitre (mL). Water bottles in the market are of different sizes and quantities, with labels like 1L, 500 mL, 250 mL, etc. This label indicates the volume of water, a water bottle can hold.
The SI unit (International System of Units) of mass is the kilogram, it is abbreviated as kg.
The SI unit of volume is the cubic meter, abbreviated as, m3.
It is important to remember that 1 m3 = 1000 L.

Matter

Mass and volume are the two properties that are possessed by all the materials. Anything that occupies space and has a mass is called matter. Mass measures the quantity of matter present in an object and Volume measures the space occupied by matter present in an object. Thus, by measuring the mass and volume of an object, we can tell that an object contains matter, and mass and volume are the two contributing factors for understanding matter. Objects are made up of materials, which are also types of matter. All the materials around us are examples of matter, like, water, bricks, glass, air, etc.

→ Object: A thing that can be seen and touched.

→ Material: Any substance which is used to create an object.

→ Hard Materials: Materials that are difficult to compress or scratch.

→ Soft Materials: Materials that can be compressed or scratched easily.

→ Transparency: The property of a material that allows the light to pass through it.

→ Transparent Materials: Materials through which an object can be seen clearly.

→ Translucent Materials: Materials through which we can see the object but not clearly.

→ Opaque Materials: Materials through which we cannot see at all.

→ Soluble Materials: Materials that disappear when mixed in water, i.e. they dissolve in water.

→ Insoluble Materials: Materials that do not disappear when mixed with water, even if we stir them for a long time.

→ Mass: It is the property that measures how heavier or lighter an object is.

→ Space: The amount of area an object occupies, which can vary depending on its shape and size.

→ Volume: The amount of space occupied by a liquid.

→ Matter: Anything that occupies space and has a mass.

Class 6 Science Notes

Measurement of Length and Motion Class 6 Notes Science Chapter 5

Class 6 Science Chapter 5 Notes Measurement of Length and Motion

This chapter deals with the concept of measurement of length, its standard units, and the correct way of measuring length. It also includes an understanding of motion and its types.

Measurement

Measurement is the method of comparison of an unknown quantity with a given known quantity. It is expressed in two parts: a number and a unit. For example, You measure the length of your study table to be 2 meters. In this example, the first part, i.e. 2 is the number and the second part, i.e. meter is the unit of measurement.

Ancient Methods of Measurement
In ancient days, people used to have the following methods or units to measure length or distance.

→ Hand span is the length between the tip of the thumb and the little finger of our hand when we stretch it as shown in Figure (a).
Measurement of Length and Motion Class 6 Notes Science Chapter 5 1

→ Yard is the length between the tip of the middle finger and the chin of an outstretched arm as shown in Figure (b). It was mainly used to measure the length of clothes and wires.

→ Footstep is the length between the big toe and the heel of the foot as shown in figure (c). This method was used to measure the distance from one point to another.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 2

→ Mutthi (fist) refers to the quantity that a person’s mutthi or a fist can hold as shown in Figure (d). It is used to measure small quantities of grains and pulses like rice, grams, wheat, etc.

→ Angul (finger) is the width of the finger as shown in Figure (e). It was used to measure very small distances. You may have heard this from your grandparents that a teacup has a height of “chaar angul”, i.e. the width of four fingers.

→ Dhanusa is an ancient unit of measuring height used in Jain literature.

→ Yojana is a measuring of distance used in ancient India.

In ancient times units like Dhanusa, and Yojana were used in measuring artifacts, architecture, and town planning. The Angola is still used by traditional craftspeople like carpenters and tailors. However, the ancient methods of measurement are really interesting but they differ from person to person.

Standard Unit of Measurement
Since, the ancient methods of measurement were inaccurate, to have a fixed value of measurement, a set of standard units of measurement is adopted. The system of units now used is known as the ‘International System of Units’ or SI units.

→ The SI unit for measuring length is meter (m).

  • 1 m = 100 cm
  • 1 cm = 10 mm

→ For measuring smaller lengths, we use units such as centimeters or millimeters.

  • 1 mm = 0.1 cm

→ For long distances, the meter is not a suitable unit, hence we define, a larger unit of length that is a kilometer (1cm).

  • 1 km = 1000 m

In some scales, you might have noticed another scale marking. This scale marking is in inches, where 1 inch = 2.54 cm. These units are used to measure one’s height.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 3

Correct Way of Measuring Length

For measuring any length, we need an appropriate scale. For example, if you want to measure the length of your pencil, you may use a 15 cm scale. Similarly, if the height of a door is to be measured, you may need a meter scale or a measuring tape. You cannot directly measure the size of your chest using a meter scale. For such measurements, flexible measuring tape, such as a tailor’s tape is more suitable. So, for measurement, the usage of the correct measuring device and way of measuring the lengths play a vital role.

Precautions while Taking Measurements
For taking measurements, we must keep the following points in mind.

→ To take measurements of the length of the object, we must put the scale along its length as shown in the figures.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 4

→ If the end of the scale is broken and we are not able to see a zero mark, then take any full mark of the scale and subtract the reading of this mark from the reading at the other end as shown in the figures.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 5

→ During measurement, the position of the eye is also very important. So, we must keep our eyes in such a way that it is exactly in front of the point where the measurement is to be taken as shown in the figure.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 6

Units of length, such as kilometer, meter, centimeter, and millimeter, begin with a lowercase letter, except at the beginning of a sentence. Their symbols km, m, cm, and mm are also written in lowercase letters and are never followed by ‘s’ for the plural. Note that a full stop is not written after the symbol, except at the end of a sentence. While writing the length, always leave a space between the number and the unit.

Measuring the Length of a Curved Line

We cannot measure the length of a curved line directly by using a meter scale. We can use a flexible measuring tape or a thread to measure the length of a curved line. If we carefully move the thread along the curved line while keeping it stretched tightly and then measure the used part of the thread by a meter scale, we get the length of the curved line.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 7
Visually challenged students use scales with raised markings that can be felt by touching them.

Describing Position

Position is nothing but the, location of an object. When the distance of an object is stated with respect to a fixed point or position, then this point is called a reference point. So, we can say that distance is the measure of how far is something from a reference point. For example, While traveling, the kilometer board that we see indicates our distance from our destination point.

Motion
If the position of an object changes concerning the reference point with time, then the object is said to be in motion. If an object is not changing its position concerning the reference point with time, it is said to be at rest.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 8

The reference point is important in deciding whether an object is in motion or at rest. If you are on a bus and consider yourself as a reference point, then other passengers on the bus are at rest as there is no change in their position concerning you. But for another reference point outside the bus (maybe a tree, a pole, a building), the passengers inside the bus are in motion because their position is changing concerning the reference point.

Types of Motion
When we see around us, we experience a lot of things moving around, for example, vehicles on a straight road, rotation of a fan, a moving bicycle, etc. Different objects show different types of motion. Some of them are stated below

(i) Linear Motion:
When an object moves along a straight line, its motion is called linear motion.
e.g. Vehicle running on a straight road, the motion of a bullet when fired, sprinters in a 100 m race, march-past of soldiers, etc.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 9

(ii) Circular Motion:
When an object moves along a circular path, its motion is called circular motion.
e.g. Hands of a clock, motion of stone in the following figure, etc.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 10

(iii) Oscillatory Motion:
When an object moves to and fro about some fixed position, its motion is called oscillatory motion.
e.g. Motion of a simple pendulum, a garden swing, etc.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 11

(iv) Periodic Motion:
If an object repeats its motion after a fixed interval of time, its motion is said to be periodic.
e.g. The motion of the minute hand of a clock, the revolution of the earth around the sun, etc.
Measurement of Length and Motion Class 6 Notes Science Chapter 5 12

All oscillatory motions are periodic but periodic motions are not always oscillatory.
Example: Motion of the minute hand of the clock (it exhibits periodic motion but not oscillatory).

→ Measurement: The method of comparing any unknown quantity with a known quantity is called measurement.

→ S.I. units: It is a universally accepted metric system of units.

→ Length: Length is the size of something from one end to the other.

→ Distance: The total length of the path from one point to another is called distance.

→ Reference: Point A reference point is a fixed point concerning which something is observed or measured.

→ Motion: An object is said to be in motion if its position changes concerning the reference point with time.

→ Linear Motion: Linear motion is when an object moves along a straight line.

→ Circular Motion: Circular motion is when an object moves along a circular path.

→ Oscillatory Motion: Oscillatory motion is when an object moves to and fro about its mean position.

→ Periodic Motion: Periodic motion is when an object repeats its motion after a fixed interval of time.

Class 6 Science Notes

Exploring Magnets Class 6 Notes Science Chapter 4

Class 6 Science Chapter 4 Notes Exploring Magnets

Playing with magnets is always fun. We see so many examples in our everyday life in which an object attracts some special materials like iron, such objects are known as magnets. Magnets can even attract or repel other magnets too. In this chapter, we will explore the interesting concepts related to it.

Magnet

The substances having the property of attracting iron are known as magnets. In our daily life observations, we have often seen certain stickers on the doors of refrigerators. The white iron boards in schools often have dusters that can be stuck to them. A pin holder has lots of pins stuck to it and a crane picks up pieces of iron from waste, etc. All these objects have a special substance called a magnet in them. Nowadays, magnets are used to make mobile devices, telephones, televisions, etc.
Exploring Magnets Class 6 Notes Science Chapter 4 1

Natural Magnet and Artificial Magnet
A magnet that is found in nature is known as a natural magnet, e.g. magnetite and lodestone, whereas the magnet that can be made by magnetizing materials like iron, cobalt, nickel, etc., is known as an artificial magnet or man-made magnet.
Exploring Magnets Class 6 Notes Science Chapter 4 2
Nowadays, artificial magnets are prepared in different shapes, e.g. bar magnets, horseshoe magnets, cylindrical magnets, ball-ended magnets, and U-Shaped magnets.

Magnetic and Non-Magnetic Materials
All the materials are not attracted by magnets. Magnets attract only certain materials. Those substances that get attracted by a magnet are called magnetic materials, e.g. iron, steel, nickel, and cobalt. Those substances that are not attracted by the magnet are called non-magnetic materials, e.g. rubber, plastic, stainless steel, feather, and leather. Magnets can make our tasks much easier, e.g. when a needle slips from our hand on the floor. To find it, we use a magnet. Since a needle is made of iron, it can be attracted by a magnet. Non-magnetic materials cannot be magnetized. It means that non-magnetic materials cannot be converted into magnets.

Poles of Magnet
When we bring a magnet close to iron filings, we see that iron filings get attracted toward a magnet. If we observe, we will find that most of the iron filings stick at the two free ends of a magnet. These free ends are called the poles of a magnet. Poles of the magnet are the regions of strongest magnetism. All magnets have two poles north pole and the south pole, irrespective of their shape. Usually, north (N) and south (S) poles are marked on the magnets.
Exploring Magnets Class 6 Notes Science Chapter 4 3
The North and south poles of a magnet always exist in pairs. The north pole and south pole of a magnet can’t exist independently or cannot be separated. If a magnet is broken into two or more pieces, each of them will have a north pole and a south pole.

Finding Direction

An interesting property of a magnet is that a freely suspended bar magnet always comes to rest in a north-south direction. Based on this property, a small device called a magnetic compass was developed in the olden days for finding directions. The end of the magnet that points towards the north is called north seeking end or north pole of the magnet and the other end that points towards the south is called south seeking end or south pole of the magnet.
Exploring Magnets Class 6 Notes Science Chapter 4 4
In the early centuries, this property of magnets was very useful for travelers. They used to suspend natural magnets with a thread to find directions. Other methods can help to find directions, e.g. By using the direction of the rising sun in the morning, we can find out the rough direction towards the east. If we stand facing east, then our left will be towards north. It may not be very exact but it will help to make out all the directions as shown in the figure.

Magnetic Compass
In the olden days, a magnetic compass was used for finding directions. A magnetic compass is a small circular box with a transparent cover on it. There is a magnet, in the shape of a needle, mounted on a pin standing on the bottom of the box. It is pivoted to rotate freely. The end of the needle which rests in the north direction is usually painted red. Below the needle, there is a dial with directions marked on it.
Exploring Magnets Class 6 Notes Science Chapter 4 5

The Earth also behaves like a giant magnet. The magnetic compass aligns with the earth’s magnetic poles such that the north pole of the magnetic compass needle always points to the earth’s north pole and vice-versa. To find the directions using a compass

  • The compass is placed at a place where we wish to know the direction.
  • The compass needle points in the north-south direction, when it comes to rest.
  • The dial of the compass is gently rotated and aligned with the north-south axis of the needle. This gives the north-south, direction.

Attraction and Repulsion between Magnets

When the north-north or south-south poles of two magnets are brought closer, they push each other away or they repel each other. It can be stated that poles repel each other.
Exploring Magnets Class 6 Notes Science Chapter 4 6
On the other hand, when the north-south or south-north poles of two magnets come closer, then they attract each other. It can be stated that unlike poles attract each other. The attractive or repulsive force that is exerted between the poles of a magnet is also known as magnetic force.

In some magnets, the north and south poles are marked as N and S while in some other magnets, the north pole is indicated by a white dot, and in some cases, the north pole is painted red and the south pole is painted blue.

→ The compass needle is also a magnet. It shows the same behavior if a magnet is brought closer to it.

→ When the North pole of a magnet is brought closer to the North pole of the compass needle, it moves away.

→ When the South pole of the magnet is brought closer to the North pole of the compass needle, it moves closer.

→ The magnetic force can pass through thin sheets of non-magnetic objects such as paper, glass, or wood.

→ Generally, the north and south poles of a magnet are marked as N and S. In some magnets, the north pole is indicated by a white dot.

→ Sometimes, the north pole of a magnet is represented by red colour and the south pole by blue colour.

Maglev train works on the principle of attraction and repulsion between magnets. It contains two sets of magnets. One set of magnets is used to repel and push the train up off the track and another set is used to move the elevated train ahead.

How to keep magnets safe?

  • Keep magnet in pairs with unlike poles on the same side.
  • Keep a piece of wood in between while storing magnets.
    Exploring Magnets Class 6 Notes Science Chapter 4 7
  • Place two pieces of soft iron across the ends.
  • Do not heat, hammer, or drop the magnets from a height.
  • Keep them away from mobiles, computers, televisions, music systems, etc.

Fun with Magnets!

Magnets can move some objects without touching them. Some of the fun experiments are given below.

→ We can make a magnetic garland by using a bar magnet which induces magnetism in the board pins, causing them to stick together.
Exploring Magnets Class 6 Notes Science Chapter 4 8
→ We can create a maze by using cardboard and plastic straws (as shown in the figure) and try to take the steel balls out of the maze by moving a magnet below the cardboard tray.
Exploring Magnets Class 6 Notes Science Chapter 4 9
→ We can also pick out a steel paper clip fallen in water by using a magnet, without making our fingers or the magnet wet.
Exploring Magnets Class 6 Notes Science Chapter 4 10

→ Bar magnet: A bar magnet is a rectangular piece of an object, made up of magnetic materials, that shows permanent magnetic properties.

→ Magnetic materials: Materials that are attracted to a magnet are called magnetic materials. For example, iron, nickel, cobalt.

→ Non-magnetic materials: Materials that are not attracted to a magnet are called non-magnetic materials. For example, wood, plastic, and rubber.

→ Poles of a magnet: The two ends of a magnet where the magnetic force is strongest are considered the two poles of a magnet.

→ Magnetic compass: A device that contains a magnetic needle that rests itself in a north-south direction. It is used to find directions.

→ Attraction: Attraction is the force that attracts two bodies to move towards each other.

→ Repulsion: Repulsion is the force that keeps the bodies away from each other.

Class 6 Science Notes

Mindful Eating: A Path to a Healthy Body Class 6 Notes Science Chapter 3

Class 6 Science Chapter 3 Notes Mindful Eating: A Path to a Healthy Body

Food in Different Regions

Food varies widely across regions due to differences in climate, culture, and available ingredients. Even within India, there is a significant variation in food. Food preferences in different regions of India are influenced by many factors, such as local crop cultivation, taste culture, and tradition.

The table below gives some traditional food items and the crops grown in different states of India.

State Locally Grown Crops Traditional Food Items Eaten Beverages
Punjab Maize, Wheat, Chickpea, Pulses Makki di roti, sarson da saag, chhole bhature, parantha, halwa, kheer. Lassi, chhach (butter milk), milk, tea.
Karnataka Rice, Ragi, Urad, Coconut Idli, dosa, sambhar, coconut chutney, ragi mudde, palya, rasam, rice. Buttermilk, Coffee, Tea
Manipur Rice, Bamboo, Soyabean Rice, eromba (chutney), utti (yellow peas and green onion curry) and singju, kangsoi.

Black Tea

All these food items have essential components required for the proper growth and development of an individual.

Components of Food

Each food item is usually made up of one or more ingredients, which we get from plants or animals. These ingredients contain some components, which are needed by our body. These components are known as nutrients. Thus, nutrients are the substances that are needed by our body to grow, function properly, and stay healthy. The major nutrients present in our food are as follows.

  • Carbohydrates
  • Proteins
  • Fats
  • Vitamins
  • Minerals

The food items based on the presence of these nutrients can be classified as

  • Energy-giving foods: These food items are mainly rich in carbohydrates and fats.
  • Body Building Foods: These food items are rich in proteins.
  • Protective Foods: These food items are rich in vitamins and minerals.

Carbohydrates
They are one of the primary sources of energy in our diet, that provide instant energy. The main carbohydrates found in our food are starch and sugars. Cereals like wheat, rice, and maize; vegetables like potato and sweet potato; fruits like banana, pineapple, and mango and glucose are some sources of carbohydrates.
Mindful Eating A Path to a Healthy Body Class 6 Notes Science Chapter 3 1

Fats
Just like carbohydrates, fats also provide energy to our body. The amount of energy given by fats is much more as compared to the same amount of carbohydrates. They are the source of stored energy. Fats can be obtained from plants as well as from animals.

(i) Plant-Based Sources of Fats:
These include nuts, such as groundnuts, walnuts, coconuts, and almonds, and seeds, such as pumpkin seeds and sunflower seeds.
Mindful Eating A Path to a Healthy Body Class 6 Notes Science Chapter 3 2

(ii) Animal Based Sources of Fats:
These include butter, ghee, milk, cream, cheese, eggs, meat and fish.
Mindful Eating A Path to a Healthy Body Class 6 Notes Science Chapter 3 3

Polar bears accumulate a lot of fat under their skin. This fat serves as an energy source. It supports them during their months-long winter sleep (hibernation), enabling them to survive without eating.

Proteins
These are body-building foods that are essential for the growth and repair of the body tissues. Proteins in our diet come from both plant and animal sources.

(i) Plant-Based Sources of Proteins:
These are obtained from plants and their products like gram, moong, tuar dal, kidney beans, peas, and soybeans.
Mindful Eating A Path to a Healthy Body Class 6 Notes Science Chapter 3 4

(ii) Animal Based Sources of Proteins:
These are obtained from animal products like milk, paneer, eggs, fish, and meat.
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Edible mushrooms are a good source of proteins. They grow mostly in dark and moist places.

Vitamins
These are a group of nutrients that are essential for the proper functioning of our body but are required in small quantities. Vitamins are essential nutrients that protect our body against diseases. They also help keep our ‘eyes, bones, teeth, and gums healthy. Some vitamins, their sources, and their functions are tabulated as follows.

Vitamins Functions Sources
Vitamin – A Keeps eyes and skin healthy. Papaya, carrot, mango, milk.
Vitamin – B1 Keeps the heart healthy and supports the body to perform various functions. Legumes, nuts, whole grains, seeds, (flax seeds, pumpkin seeds) milk products.
Vitamin – C Helps the body to fight against diseases. Amla, guava, green chilli, orange, lemon, tomato.
Vitamin – D Helps the body to absorb calcium for bone and teeth health. Exposure to sunlight, milk, butter, fish, eggs, edible mushrooms.

Vitamin D can be naturally produced by our body upon exposure to sunlight.

Minerals
These are essential for proper growth of the body and to maintain good health. Like vitamins, these are also needed by our body in small amounts, e.g. iron, calcium, iodine, etc. Some minerals along with their sources and functions are tabulated below.

Minerals Functions Sources
Calcium Keeps bones and teeth healthy. Milk/Soya Milk, Curd, Cheese, Paneer.
Iodine Helps to perform physical and mental activities. Seaweed, water chestnut (singhada), iodized salt.
Iron An important component of blood. Green leafy vegetables, beetroot, pomegranate.

In addition to these essential nutrients, our body needs dietary fibers (roughage) and water.

Water
It is one of the major constituents of our food. About 70% of the human body is made up of water. One can get water in the following ways.

  • Most of the water can be obtained from liquids like water, milk, and tea.
  • In addition, water is also obtained from fruits and fresh vegetables.
  • Even while cooking, a lot of water is added to the food.

Water performs the following functions in our body:

  • It helps our body to absorb nutrients from food.
  • It removes waste from the body as urine and sweat.
  • Hence, one should drink plenty of water to stay healthy.

Roughage (Dietary Fibre)
It is the fibrous matter present in food that cannot be digested. Roughage in our food is mainly provided by suitable plant products. Green leafy vegetables, fresh fruits, whole grains, pulses, and nuts are the main sources of roughage. Roughage is also called dietary fiber (the fiber that can be eaten). It does not provide any nutrients to our body, but it is an essential component of our food and adds to its bulk. It helps our body to get rid of undigested food and ensure smooth passage of stool.

Balanced Diet

The total amount of food that a person eats during an entire day is called their diet. A balanced diet is a diet that contains the proper amount of all the nutrients along with a good amount of roughage and water. It provides the body with all the energy and fulfills various nutrient requirements needed for proper functioning. A balanced diet is not the same for everyone. The type and amount of nutrients in a diet may vary according to the age, gender, physical activity, health status, and lifestyle of a person. This can be explained by the following examples.

  • Sports persons need proteins in larger quantities to build their muscles.
  • Children in their growth phase require more/the right amount of protein for proper growth and development.

A balanced diet is crucial for maintaining good health but consuming packaged food like potatoes, wafers, candy bars, and carbonated drinks can significantly deteriorate Cone’s health and can cause obesity. Such types of food are often referred to as junk food. These food items have high calories due to high sugar and fat content. Moreover, they contain very low amounts of proteins, minerals, vitamins, and dietary fibers.

Package food items must include information about the nutrients on their labels, specifying the amount of each nutrient. Sometimes, more nutrients are added to the food during processing (fortification) to improve its nutritional quality. Iodized salt and some baby foods are examples of fortified foods. The Food Safety and Standard Authority of India (FSSAI) is a government agency that regulates food quality in India.

Culinary Practices and their Impact on Nutrients in Food
In addition to a balanced diet, mindful cooking habits are vital for maintaining good health. The cooking practices also known as culinary practices, have evolved leading to significant differences between modern and traditional approaches. As earlier most of the cooking was done using a chulha and sil-batta, but now it has been replaced by a modern gas stove and an electrical grinder. These changes may be due to factors such as technological development, improved transportation, and better communication. However, it is important to note that regardless of the cooking practice used, some nutrient loss can occur during food preparation.

Loss of Nutrients in Food
We all know that cooking improves the taste of food and makes it easier to digest. At the same time, cooking also results in the loss of certain nutrients. So, while cooking one should remember the following important things.

  • Some nutrients like vitamin C and others are lost during cooking due to high heat.
  • Washing cut or peeled fruits and vegetables may also result in the loss of some vitamins.
  • Repeated washing of rice and pulses may result in the loss of some vitamins and minerals present in them.
  • Consuming food that lacks vitamins and minerals for a long time can lead to several diseases.

Coluthur Gopalan (1918-2019) pioneered nutrition research in India. He analyzed over 500 Indian foods and recommended diets suited to the Indian context. He identified widespread deficiencies in protein, energy, and other nutrients, leading to the implementation of the Mid Day Meal Programme in 2002, now known as the ‘PM Poshan’ initiative. This program provides balanced meals in government-run and aided schools, improving the health and nutrition of millions of children across the country.

Deficiency Diseases

The diseases that occur due to the lack of specific nutrients in our diet over a long period are called deficiency diseases. Some diseases caused due to the deficiency of vitamins and minerals are tabulated below.

Vitamins/Minerals Deficiency Diseases/Disorder Symptoms
Vitamin-A Loss of vision Poor vision, loss of vision in darkness (night blindness), sometimes complete loss of vision.
Vitamin-B1 Beri-Beri Swelling, tingling, or burning sensation in feet and hands, trouble in breathing.
Vitamin-C Scurvy Bleeding gums, slow healing of wounds, low immunity.
Vitamin-D Rickets Soft and bent bones.
Calcium Bone and tooth decay Weak bones, tooth decay
Iodine Goitre Swelling at the front of the neck.
Iron Anaemia Weakness, shortness of breath.

The link between deficiencies and their associated vitamins or minerals can be clarified through the following cases.

  • Case 1: In earlier times, during long voyages, sailors often suffered from bleeding and swollen gums (scurvy). During a voyage in 1746, Scottish physician James Lind observed that sailors, who consumed lemons and oranges recovered from these symptoms.
  • Case 2: In the 1960s, Indian scientists found that among the human population in the Himalayan region and the Northern plains of India, symptoms of swelling at the front of the neck (goiter) were prevalent.

As per norms of the Government of India, an effort was made to supplement common salt with iodine for preparing iodized salt. Consumption of iodized salt visibly reduced the above symptoms. These symptoms were due to a deficiency of iodine in the soil of this region resulting in a lack of iodine in the local food and water supply.

Nutrients like salt can be obtained either from rocks or from seawater. For harvesting salt from sea water a tribal community named Agariyas practices traditional salt farming methods. Similarly, the Apatani tribe of Arunachal Pradesh produces a salt called tap to fulfill their dietary requirements.

To prevent such deficiency and diseases, it is important to consume foods rich in vitamins and minerals. Recently, millets have gained popularity due to their high content of vitamins, minerals (iron, calcium), and dietary fibers, offering numerous health benefits.

Millets: Nutrition-rich Cereals

Millets are highly nutritious grains that have been an integral part of the Indian diet for centuries. Jowar, bajra, ragi, and Sanwa (barnyard millet) are examples of millets. These are native crops of India and can be easily cultivated in different climatic conditions. Millets are often referred to as nutri-cereals as they are rich in essential nutrients. They also contribute significantly to a balanced diet required for the normal functioning of our body. Having a diet that consists of locally grown plant-based food is not only healthy but also beneficial for the environment and the planet. The journey of all farm-produced foods including, these local and plant-based options, can be understood through the concept of food miles.

Food Miles: From Farm to Our Plate
The entire distance traveled by any food item from the producer to the consumer is known as its food miles. The food produced on farms reaches our plates through various steps. These steps involve a considerable amount of time and effort of many people. For example, the entire process of making the chapati can be understood from the image given below.
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Benefits of Reducing Food Miles
Reducing food miles means decreasing the distance of food travel from the place of its production to the consumer. This practice provides the following benefits.

  • It helps to cut down the cost and pollution associated with food transport.
  • It supports local farmers and businesses which strengthens their economy.
  • It ensures the food is fresher and more nutritious.

→ Carbohydrates: They provide energy to our body.

→ Culinary practices: Cooking practices are also called culinary practices.

→ Deficiency diseases: The disease, which occurs due to the lack of specific nutrients in our diet over a long period.

→ Fats: These are the storehouse of energy in our body.

→ Food Components: The major nutrients in our food.

→ Food Miles: The entire distance traveled by food item from producer to the consumer.

→ Iodised Salt: Salt that contains small amounts of iodine.

→ Millets: Jowar, bajra, ragi, and Sanwa are called millets.

→ Minerals: Essential for proper growth of the body and to maintain good health.

→ Nutrients: The fundamental components of food, that provides nourishment to the body.

→ Proteins: These are body-building food that helps in repairing and maintaining the body tissues.

→ Rickets: Disease caused by the deficiency of vitamin D.

→ Roughage: These are dietary fiber that forms bulk and help in the removal of undigested food.

→ Scurvy: Disease caused by the deficiency of vitamin C.

→ Vitamins: These are essential nutrients that protect our body against diseases.

Class 6 Science Notes