Start by reviewing these Class 8 Science Curiosity Solutions Chapter 5 Exploring Forces Question Answer to strengthen your knowledge.
Class 8 Science Curiosity Chapter 5 Question Answer
Class 8 Science Ch 5 Exploring Forces Question Answer
Class 8 Science Chapter 5 Exploring Forces Question Answer (InText)
Question 1.
Why does it feel harder to pedal a bicycle when going uphill than on the flat ground? (Page 62)
Answer:
It feels harder to pedal a bicycle uphill because we are working against the force of gravity in addition to friction. When going uphill, we must push the bicycle and our body upward, which requires more effort than moving on flat ground, where gravity doesn’t oppose our motion as much.
Question 2.
Why is it easier to slip on a flat ground? (Page 62)
Answer:
It is easier to slip on flat ground when the surface is smooth or wet because friction is reduced. Friction is the force that prevents slipping by resisting motion between surfaces. On a smooth or slippery flat surface, this frictional force becomes very low, making it harder for our feet to grip the ground and we may easily slip.
Question 3.
Why do we feel light or like we are floating just after our swing reaches its highest point and begins to come down? (Page 62)
Answer:
We feel light or like we are floating just after the swing reaches its highest point and begins to come down because, at that moment, the force of gravity is pulling us downward while the swing is momentarily weightless. Our body is in a brief state of free fall, where the support force from the swing seat reduces for an instant, creating a sensation of weightlessness.
Question 4.
Whenever there is a change is speed or direction or a change in shape, a force is acting on the object. Is it true? (Page 65)
Answer:
Yes, it is true. Whenever there is a change in an object’s speed, direction or shape, a force is acting on it. Force is responsible for producing or changing motion and also for deforming objects. So, any such change is evidence that a force is being applied.
Question 5.
Is there any other contact force apart from muscular force and frictional force? (Page 67)
Answer:
Yes, apart from muscular force and frictional force, another contact force is the normal force. It is the force exerted by a surface that supports the weight of an object resting on it and acts perpendicular to the surface. For example, when a book rests on a table, the table exerts an upward normal force on the book.
Question 6.
Is it true that the force of friction will be greater if the surfaces on which the bodies are sliding are rough? (Page 68)
Answer:
Yes, it is true. The force of friction is greater when the surfaces in contact are rough because rough surfaces have more irregularities that interlock with each other, increasing resistance to motion. Smooth surfaces have fewer irregularities, so they produce less friction.
Question 7.
Is it essential for an object applying force on another object to always be in contact with it ? (Page 69)
Answer:
No, it is not essential for an object applying force to always be in contact with another object. Non-contact forces like gravitational force, magnetic force, and electrostatic force can act from a distance without physical contact. For example, the Earth pulls objects toward it due to gravity without touching them.
Question 8.
Are electric charges of two kinds? (Page 71)
Answer:
Yes, electric charges are of two kinds, positive and negative. Objects with like charges repel each other, while objects with unlike charges attract each other.
Question 9.
Why do all the objects fall towards the earth? Is there any force which acts on them? What exerts this force? (Page 72)
Answer:
All objects fall toward the Earth because of a force called gravity. This is a non-contact force that pulls all objects toward the center of the Earth. It is exerted by the Earth itself on every object that has mass. Gravity is the reason things fall down when dropped.
Question 10.
Does the earth pull every object with equal force? (Page 72)
Answer:
No, the Earth does not pull every object with equal force. The gravitational force depends on the mass of the object, i.e. the greater the mass, the stronger the force with which the Earth pulls it. So, heavier objects experience a stronger gravitational pull than lighter ones.
Question 11.
What is the difference between weight and mass? (Page 75)
Answer:
Mass is the amount of matter in an object and is measured in kilograms (kg). It is constant and does not change with location. Weight, is the force with which the Earth pulls an object due to gravity. It is measured in newton (N) and can change depending on the strength of gravity at a place.
Question 12.
If some objects are placed on water, some of them float, while others fall to the bottom. The gravitational force of earth is acting on all objects, then why don’t all objects fall to the bottom? (Page 76)
Answer:
Although the gravitational force of the Earth acts on all objects, not all objects fall to the bottom because another force called upthrust or buoyant force also acts on them when they are placed in water. Whether an object floats or sinks depends on the balance between gravitational force and upthrust. If the upthrust is greater than or equal to the object’s weight, it floats. If the object’s weight is greater than the upthrust, it sinks. So, floating or sinking depends on the density of the object compared to water and the net force acting on it.
Exploring Forces Class 8 Questions and Answers (Exercise)
Question 1.
Match items in column A with the items in column B.
| Column A (Types of force) | Column B (Example) |
| A. Muscular force | 1. A cricket ball stopping on its own just before touching the boundary line |
| B. Magnetic force | 2. A child lifting a school bag |
| C. Frictional force | 3. A fruit falling from a tree |
| D. Gravitational force | 4. Balloon rubbed on woollen cloth attracting hair strands |
| D Electrostatic force | 5. A compass needle pointing North |
Answer:
| Column A (Types of force) | Column B (Example) |
| A. Muscular force | 2. A child lifting a school bag |
| B. Magnetic force | 5. A compass needle pointing North |
| C. Frictional force | 1. A cricket ball stopping on its own just before touching the boundary line |
| D. Gravitational force | 3. A fruit falling from a tree |
| D Electrostatic force | 4. Balloon rubbed on woollen cloth attracting hair strands |
Question 2.
State whether the following statements are True or False.
(i) A force is always required to change the speed of motion of an object.
(ii) Due to friction, the speed of the ball rolling on a flat ground increases.
(iii) There is no force between two charged objects placed a small distance apart.
Answer:
(i) True, A force is needed to increase or decrease the speed of an object.
(ii) False, Friction always opposes motion, so it reduces the speed of the ball.
(iii) False, There is an electrostatic force between charged objects, even without contact.
Question 3.
Two balloons rubbed with a woolen cloth are brought near each other. What would happen and why?
Answer:
When two balloons are rubbed with a woolen cloth and brought near each other, they repel each other because both acquire similar electric charges through rubbing. Since like charges repel each other, the electrostatic force between the two similarly charged balloons causes them to push away from each other.
Question 4.
When you drop a coin in a glass of water, it sinks, but when you place a bigger wooden block in water, it floats. Explain.
Answer:
The coin sinks because its density is greater than that of water, and the upthrust (buoyant force) acting on it is not enough to balance its weight. On the other hand, the bigger wooden block floats because it is less dense than water and the upthrust acting on it is greater than or equal to its weight, which helps it stay afloat. So, whether an object sinks or floats depends on its density and the upthrust acting on it.
Question 5.
If a ball is thrown upwards, it slows down, stops momentarily and then falls back to the ground.
Name the forces acting on the ball and specify their directions
(i) during its upward motion
(ii) during its downward motion
(iii) at its topmost position
Answer:
(i) The force of gravity acts downward, opposite to the direction of motion. This is why the ball slows down.
(ii) Only the force of gravity acts downward, in the same direction as the motion, so the ball speeds up as it falls.
(iii) The ball is momentarily at rest, but gravity still acts downward, and it causes the ball to begin falling back.
Question 6.
A ball is released from the point Pand moves along an inclined plane and then along a horizontal surface as shown in the fig. It comes to stop at the point A on the horizontal surface. Think of a way so that when the ball is relased from the same point P, it stop (i) before the point A (ii) after crossing the point A.
Answer:
(i) To make the ball stop before point A, increase the roughness (friction) of the horizontal surface between P and A Higher friction will slow the ball down more quickly, making it stop before reaching point A.
(ii) To make the ball stop after crossing point A reduce the friction on the horizontal surface (e.g. make it smoother), so the ball experiences less resistance and rolls further before stopping.
Question 7.
Why do we sometimes slip on smooth surfaces like ice or polishing floors? Explain.
Answer:
We sometimes slip on smooth surfaces like ice or polished floors because these surfaces have very low friction. Friction is the force that helps our feet grip the ground and prevents slipping. On smooth or slippery surfaces, this frictional force is greatly reduced, so our feet cannot hold onto the surface properly, making us lose balance and slip.
Question 8.
Is any force being applied to an object in a non-uniform motion?
Answer:
Yes, if an object is in non-uniform motion, a force is definitely being applied to it. Non-uniform motion means the object’s speed or direction is changing and any change in speed or direction is caused by a force acting on the object. So, the presence of non-uniform motion indicates that a force is acting.
Question 9.
The weight of an object on moon becomes one-sixth of its weight on the earth. What causes this change? Does the mass of the object also become one-sixth of its mass on the earth?
Answer:
The weight of an object on the Moon becomes one-sixth of its weight on the Earth because the Moon’s
gravitational force is much weaker than Earth’s (about one-sixth). Weight depends on gravity, so it changes with location.
However, the mass of the object remains the same . because mass is the amount of matter in an object and does not change with gravity or location.
Question 10.
Three objects 1, 2 and 3 of the same size and shape but made of different materials are placed in the water. They dip to different depths as shown in fig. If the weights of the three objects 1, 2 and 3 are w1 , w2 and w3, respectively, then
(i) w1 = w2 = w3
(ii) w1 > w2 > w3
(iii) w2 > w3 > w1
(iv) w3 > w1 > w2
Answer:
All three objects have the same size and shape but are made of different materials, so their weights are different. In water, the object that sinks more must be heavier, because it needs more upthrust to balance its weight. From the figure, object 1 is submerged the most, so it is the heaviest, while object 3 floats the most, so it is the lightest. Therefore, the order of their weights is w1 > w2 > w3.
Hence, option (ii) is correct.
Class 8 Science Chapter 5 Question Answer (Activities)
Activity 1 (Page 63)
Aim
To experience the push and pull due to a force. Materials Required A cardboard box, a long rope.
Procedure
- Take a large cardboard box.
- First try pushing it.
- Then tie it to a rope and try pulling it.
- Finally, try lifting it upwards.
Conclusion
In all the above actions performed, a force of push or pull was involved. Otherwise the box could have not been moved at all.
Viva Questions
- What is force?
- If an object is moving at a constant speed, is any force acting on it?
Activity 2 (Page 64)
Aim
To understand the different actions of force and their effects.
Materials Required
A ball and a bat, a balloon, a bicycle.
Procedure
| S.No. | Action | Push/Pull | Effect |
| 1. | 1. Holding a bicycle from behind to stop it. | Pull | The speed of the bicycle decreases and then stops. |
| 2. | 2. Hitting a moving ball with a bat. | Push | The direction of the moving ball changes |
| 3. | 3. Pressing an inflated balloon. | Push | The balloon undergoes a change in shape. |
Conclusion
From the above actions we could see that when force is applied on an object, it can either change the state of its motion, change its direction or change its shape.
Viva Questions
- When you push a table, it moves. Which type of force is applied?
- If an object is moving at a constant speed, is any force acting on it?
Activity 3 (Page 67)
Aim
To understand the force of friction.
Materials Required
An empty box, a table or the floor.
Procedure
- Take an empty box, like a lunchbox or a pencil box.
- Place it on a table or on the floor and give it a push.
- Now, give it a push from the opposite direction as well.
Conclusion
On pushing the object from either side, it moves a certain distance and then comes to a stop. This happens due to the frictional force acting between the surface of the table or the ground and the box.
Viva Questions
- What causes friction between two surfaces?
- Is friction a contact or non-contact force?
Activity 4 (Page 68)
Aim
To understand the nature of the frictional force.
Materials Required
An empty box, various surfaces like glass, wood, ceramic tile and sand.
Procedure
- Take an empty box as in activity 3.
- Place the box over all the above mentioned surfaces.
- Give them a push as mentioned in activity 3.
Conclusion
In each of the surfaces, the same pushing force on the box causes the box to move by a different distance. More rough the surface is, less is the distance travelled by the box before coming to a stop.
Viva Questions
- Give one example where friction is undesirable.
- Why do we oil machine parts?
- Can friction ever be completely removed? Why or why not?
Activity 5 (Page 69)
Aim
To understand the nature of magnetic force.
Materials Required
Two ring magnets, a wooden stick.
Procedure
- Hold the wooden stick in a vertical position.
- Insert one ring magnet onto the stick.
- Now insert the other magnet onto the stick such that the like poles face each other.
- Now push the second magnet towards the first magnet.
- Now reverse the pole of the second magnet.
- Then reverse the poles of both the magnets.
Conclusion
When the magnets are inserted such that their like poles are facing each other, the second magnet floats. When the magnet is given a push towards the first magnet, a force is experienced by us. Now when one of the poles are reversed, the second magnet sticks to the first magnet and finally when both the poles are reversed, the second magnet again floats over the first magnet.
Viva Questions
- Can magnetic force act through air or paper? Why?
- Which material is attracted by a magnet: wood, plastic or iron?
- Give two examples of magnetic materials.
Activity 6 (Page 70)
Aim
To understand the nature of electrostatic force.
Materials Required
A plastic scale or a plastic straw, a piece of polythene and some small pieces of paper.
Procedure
- Rub the plastic straw or scale vigorously with the polythene.
- Do not touch the rubbed part with any metal object or your hands.
- Now bring the rubbed part of the scale or the straw near the small pieces of paper and make sure not to touch them with your hands.
Conclusion
The pieces of paper stick to the surface of the rubbed part of the scale or straw when brought close to it. This happens due to the fact that, when two objects are rubbed against each other, charges build up on the surfaces which are called static charges and the objects which acquire the static charges are called charged objects.
Viva Questions
- Is electrostatic force a contact or non-contact force?
- Can electrostatic force exist between two objects placed in a vacuum? Why or why not?
- Why does dust sometimes stick to the screen of a television?
Activity 7 (Page 70)
Aim
To understand the different types of charges.
Materials Required
Two balloons, a length of thread, a woolen cloth.
Procedure
- Inflate two balloons and hang them in such a way so that they don’t touch each other.
- Rub both the balloons with a woolen cloth and release them.
- Make sure not to touch the rubbed balloons with your hands.
- Now bring the rubbed woolen cloth near one of the balloons.
Conclusion
The two similarly charged balloons repel each other, while the charged balloon and the woolen cloth with which the balloon was rubbed attract each other. Therefore, there are two different kinds of charges, like charges repel and unlike charges attract each other.
Viva Questions
- What is meant by static electricity?
- If a plastic pen rubbed on hair attracts paper bits, what type of force is responsible? Can it act through a medium like air?
- Why can’t we see electrostatic forces easily in our day-to-day life, even though they are always present?
Activity 8 (Page 71)
Aim
To understand the nature of gravitational force.
Materials Required
A ball, an open space like a park or a garden.
Procedure
- Take a ball on your hands.
- Throw the ball vertically upwards and observe its motion.
- Now throw the ball even harder and again watch its motion.
Conclusion
The ball first goes up, and then after coming to a stops, it falls towards the earth. In the case where the ball is thrown harder, even though it goes up a greater distance, still it finally falls back towards the earth. This means that the earth attracts objects towards itself with a force which is known as the gravitational force.
Viva Questions
- How can you conclude that the gravitational force is a non-contact force?
- What keeps the planets in orbit around the Sun?
- Can the gravitational force be repulsive?
Activity 9 (Page 73)
Aim
To measure the weight of different objects using a spring.
Materials Required
A spring, a lunch box, a pencil box, a stone.
Procedure
- Hang one end of the spring from a nail and hang different weights, one by one, from the other end of the spring.
- Observe the elongation of the spring in each of the cases.
Conclusion
When an objects hung from the spring, the spring stretches due to the gravitational pull of the objects by the Earth. We see that the stretch of the spring is different for different objects. This indicates that the earth pulls different objects with a different amount of force.
Viva Questions
- Why does a person weigh differently on different planets?
- Why do astronauts feel weightless in space?
- Why do objects weigh less on the Moon than on Earth?
Activity 10 (Page 73)
Aim
To observe the scale of a spring balance.
Materials Required
A spring balance.
Procedure
- Observe the scale of the spring balance as indicated in the figure.
- Find the maximum weight that the spring balance can measure.
Conclusion
The spring balance can measure the maximum weight of an object up to 10 N.
Viva Questions
- On what principle does a spring balance work?
- What kind of force does a spring balance use to measure weight?
Activity 11 (Page 74)
Aim
To identify the smallest weight the spring balance can measure.
Materials Required
A spring balance.
Procedure
- Observe the bigger marks on the spring balance indicated in activity 10.
- Now observe how many smaller marks are there between the bigger marks.
Conclusion
The weight difference indicated from 0N to 1N or from 1N to 2N is IN and there are five small divisions between two bigger divisions and one small division can read 0.2N. Hence the smallest weight the spring balance can measure is 0.2N.
Viva Questions
- What causes the pointer of a spring balance to move?
- What happens to the reading of a spring balance if it is taken to the Moon?
- A spring balance shows a reading of 10 N. What does this tell us about the object suspended?
- If two identical objects are hung one after the other, how will the spring balance reading change?
Activity 12 (Page 74)
Aim
To measure the weights of a few objects using a spring balance.
Materials Required
A spring balance, some materials having weight.
Procedure
- Hang a pencil box with a string from the hook at the lower end of a spring balance and note down its weight as shown in the spring balance.
- Now, hang another material, like a partially filled water bottle and again note its weight as shown in the spring balance.
Conclusion
The readings of the spring balance is different for the two different objects which indicates that the weight of different materials are different.
Viva Questions
- Why does the pointer of a spring balance return to zero after removing the object?
- How does the extension of the spring change with the weight applied?
- What will happen if a spring balance is overstretched?
Activity 13 (Page 76)
Aim
To understand the concept of upthrust.
Materials Required
An empty plastic bottle, a bucket full of water.
Procedure
- Place an empty plastic bottle on the surface of bucket filled with water.
- Try to push the bottle inwards.
Conclusion
The bottle bounces up indicating that there is some kind of an upward force acting on the bottle when it is pushed down inside a liquid such as water. This force is known as the upthrust.
Viva Questions
- Is upthrust a contact or non-contact force?
- A stone appears lighter in water than in air. Why?
- Who discovered the concept of buoyant force?
- What is the relation between upthrust and the volume of the object immersed?
- Why is it easier to lift a bucket underwater than in air?