# DAV Class 6 Science Chapter 6 Notes – Measurement and Motion

These DAV Class 6 Science Notes and DAV Class 6 Science Chapter 6 Notes – Measurement and Motion act as excellent revision resources, particularly in preparation for board exams.

## Measurement and Motion Class 6 DAV Notes

→ Physical Quantities: Measurable quantities are called physical quantities.

→ Measurement: Measurement is a process of comparison of an unknown quantity with some known fixed quantity. The fixed quantity is called the unit of measurement.

→ SI Unit: SI unit is also known as International System of Units. It is a system of internationally accepted and agreed units, of various physical quantities. Such units are known as standard units.

→ Basic Physical Quantities: There are three basic physical quantities, viz. length, time and mass.

• SI Unit of length = metre (m)
• SI Unit of time = second (s)
• SI Unit of mass = kilogram (kg) → Direct Measurement: When the object to be measured is directly measured with the given scale, it is called direct measurement. Example: measuring the length of a desk with the help of a metre scale.

→ Indirect Measurement: Sometimes, the object to be measured is first measured with a reference material. The reference material, in turn, is measured directly to arrive at the result. This process of measurement is called indirect measurement. Example: measuring the length of a curved line with the help of a thread and then measuring the length of the thread by a scale.

→ Correct Steps to Measure Length:

→ The scale should be placed in such a way that its edge is along and parallel to the length which is being measured.

→ The zero mark of the scale should coincide with one end of the length to be measured.

→ The position of eye should be vertically above the point and in line with, the reading to be taken. Change of the eye position would give wrong reading.

→ Womout or broken scale should not be used.

→ Time: Duration of an event is measured in time.

→ Pendulum Clock: A pendulum of a given length always completes an oscillation in a fixed time. This has been the basis of working of pendulum clock. Other clocks: like analog watches or digital clocks; also work on the same principle, i.e. work on the oscillation of some oscillating device.

→ Stop Watch: It is a special watch which can be started and stopped as per need. This is used for measuring the time for short duration activities; like running.

→ Rest: If an object does not change its position with respect to its immediate surrounding it is said to be at rest.

→ Motion: If an object changes its position with respect to its immediate surrounding it is said to be in motion. In other words, the change of position of an object: with change in time is called motion.

→ Rectilinear Motion: If an object changes its position along a straight line path, it is said to be in rectilinear motion.

Curvilinear Motion: If an object changes its position along a curved path, it is said to be in curvilinear motion.

→ Rotation: If an object moves around a fixed axis; without changing its position; its motion is called rotation.

→ Revolution: If an object moves around a fixed axis; continuously changing its position; its motion is called revolution. Revolution usually happens on a nearly circular path and hence is also called circular motion.

→ Periodic Motion: If a motion repeats itself at regular interval, it is called periodic motion. Non-periodic Motion: If a motion either does not repeat itself, or does the repetition in a random irregular manner, it is called non-periodic motion.

→ Oscillatory Motion: If an object moves to and fro on the same path in a regular manner, its motion is called oscillatory motion.

→ Force: A push or a pull is called force.
Effects of Force:

Force can stop motion.
Force can produce motion.
Force can change the direction of motion.
Force can change the speed of an object.
Force can change the shape and size of an object.

→ Physical Quantities: Quantities which can be measured are called physical quantities.

→ Motion: The change of position of an object with change in time is called motion.

→ Rectilinear Motion: The motion which happens on a straight line.

→ Curvilinear Motion: The motion which happens on a curved path.

→ Rotation: The motion in which an object moves around fixed axis but the position of the object does not change.

→ Revolution: The motion in which an object moves on a circular path or nearly circular path is called circular motion or revolution.

→ Periodic Motion: When a motion repeats itself at regular intervals.

→ Non-periodic Motion: When a motion either does not repeat itself or repeats at irregular intervals.

→ Oscillation: When an object moves to and fro on a fixed path at regular intervals; its motion is called oscillation.

→ Time: The duration of an event is measured in time.

→ SI Unit: Internationally accepted and agreed unit of a physical quantity is called the SI unit of that quantity.

→ Force: A push or a pull is called force.