Motion and Measurement of Distances Class 6 Notes CBSE Science Chapter 10 [Free PDF Download]

1. A body is said to be at rest when the body/object remains stationary at its place and does not change its position.

2. To go from one place to another, different modes of transport are used. In ancient days, people used the length of a foot, the width of a finger, as units of measurement. This led to lots of confusion and the need to develop a uniform system of measurement. The International System of Unit also called SI unit is accepted all over the world. The unit of length in SI unit is metre.

3. Rectilinear motion is the motion of the body in a straight line.

4. In a circular motion, a body moves in such a way that its distance from a fixed point remains the same.

5. Periodic motion is the motion that repeats itself after some $T$ interval of time.

6. Measurement of an object consists of: Its unit of measurement and the number of units that the object measures.

7. Conventional Methods: They give approximate measurement.

1. Handspan: It is the distance  between the tip of the thumb and little finger. 

2. Cubit: Length taken from the tip of the middle finger and elbow.

3. Arm length: Length taken from shoulder to the tip of the middle finger.

4. Footstep: It is the distance covered in a step.

8. Disadvantages: Differed from person to person and lacked precision.

9. Why do we need standard units of measurement?

The conventional units such as hand span, foot, footstep, cubit etc. varied. They used to depend upon the size of an individual's hand, foot, and body parts, hence such units caused a lot more confusion in measurements.

10. Standard Units of Measurement: These are the units for measuring any quantity completely and uniformly. Some standard units for measuring, length-metre, mass-kilogram, time-second.

11. RULES FOR WRITING SYMBOLS OF UNITS

1. Symbols for standard units are written in small letters.

2. Symbols are not written in the plural.

12. Motion:  When the position of a body changes with the passage of time, the body is said to be in motion. 

Types Of Motion:

1. Linear Motion: Linear motion is of two types:

1. Straight line motion: When the object moves from one position to another along a straight line. For example: Group of ants moving in a straight line.

2. Curvilinear Motion: When the object moves along curved lines. For example: a car travelling along a curved road.

2. Random Motion: When a body starts moving from one position to another and changes its direction in an irregular manner, then the body is said to be in random motion. For example, Insects flying randomly in the garden.

1. Circular Motion: When the object moves in a circular path in relation to its own axis or around a fixed centre. An object remains at the same distance from a fixed point which is the center of the path of the motion. Two types of circular motion:

2. Revolution: Revolution: When the object moves around a fixed center. For example, Earth revolves around the sun in its orbit.

3. Rotation: When the object moves in a circular path with respect to its own fixed axis. For example, the blades of a moving fan, windmill, etc. Rotation is bound to the central axis. And the extended parts attached to the rotating axis are in revolutionary motion.

4. Vibratory Motion: When the object moves in to and fro very fast. For example, when strings of a guitar are plucked.

5. Oscillatory motion: Object oscillates to and fro along the same path and with the constant speed. The time taken by an object to complete one oscillation is the same, irrespective of how many oscillations the object takes. For example, human heartbeat, a pendulum of a clock etc.

6. Periodic motion: The body is said to be in periodic motion when it repeats at regular intervals of time. For example, the heartbeat of a person, the hands of a clock.

7. Non-periodic Motion: The object is said to be under non-periodic motion when it does not repeat its motion at regular intervals of time.

8. Mixed motion: When more than one type of motion occurs at the same time. For example, a cricket ball when bowled shows linear and spin motion as well.

9. Resultant motion: The resultant motion is the motion that results in another kind of motion. For example, the wheels of a bicycle rotate about its axis which results in the linear motion of the bicycle on the road.

10. Random motion: The motion irrespective of any sequence or direction is a random motion. For example, a buzzing bee, a football player on the field.

11. Uniform Motion: The body is said to be in uniform motion when it covers equal distance in an equal interval of time. For example, the motion of the hand of a clock.

12. Non-uniform Motion: The body is said to be non-uniform when it covers unequal distances in equal intervals of time. For example, the motion of a bus along a path.