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1. Class 9
Chapter 1.Motion
THE AW

2. Introduction
When an object changes its position w’r’t a stationary object , then the object is said to be in motion.
The quantities which can be measured are known as physical quantities. Eg. Speed , Time , Distance , Mass
,etc.
Physical Quantity = Magnitude + Unit
There are different system of units which are used to measure physical quantities.
i. CGS
ii. MKS
iii. FPS
iv. SI ( International System of Units )

3. Introduction
Basic units are the fundamental units . They are independent and they are not derived from other units.
There are 7 basic units :-
◦ Length Metre – m
◦ Mass Kilogram – kg
◦ Time Second – s
◦ Temperature Kelvin – K
◦ Current Ampere – A
◦ Amount of substance Mole – mol
◦ Luminous Intensity Candela - Cd

4. Introduction
S I units ;-
Derived Units are those units which are made up of seven fundamental units . Eg. Speed , Velocity , Weight ,
force , etc.
CGS , MKS and FPS systems are almost neglected from the world but some country like US , Liberia and
Myanmar still use FPS system of units .
CGS MKS FPS SI Unit
Length cm m foot m
Mass g kg pound kg
Time s s s s

5. Types of Motion
1. Linear Motion : - When a body travels in a straight line , it is said to be in linear motion . It
is also known as 1-D motion.
2. Circular Motion : - When a body travels in a circular motion , it is said to be in circular
motion.

6. Distance and displacement
Distance is the actual path covered by the body irrespective of the direction in which the body
travels . Displacement is the shortest path from an initial point to the final point
D i s p l a c e m e n t
D i s ta n c e

7. Distance and displacement
Distance < Displacement
Distance = Displacement
But Distance ∡ Displacement
Distance is a scalar quantity. [Scalar quantities are those which have only magnitude but no
direction. Eg. Speed , Mass , Time ]
Displacement is a vector quantity [ Vector quantites are those which have both magnitude and
direction ].

8. Distance and displacement
Distance Displacement
• It is the actual path covered by the body. • It is the shortest path covered by the body.
• Scalar quantity • Vector quantity
• For a moving body, distance is always +ve. • Can be ‘0’ , ‘+ve’ or ‘-ve’ .
• Denoted by ‘s’ • Denoted by ‘d’
• s = S × t • d = v × t
• SI unit is ‘m’. • SI unit is ‘m’.

9. Types of displacement
Displacement can be of 3 types :-
Positive Displacement :- When a body moves to the right of initial point and the displacement > 0 .
Negative Displacement :- When the body moves to the
Zero Diplacement