# Science Class 9 Motion Chapter 8 Study Notes for Self Study

Class 9 Science Motion Chapter 8 Study Notes are available here for students and teachers for education purpose. Here are all formulas of physics class 9 motion chapter 8

Contents

## Class 9 Science Chapter 8 “Motion”

Class 9 Science Chapter 8 is “Motion”. This eighth chapter of Class 9 Science is very useful for exam point of view. This chapter consists of the topics – SI Unit, Motion, Rest, Distance, Displacement, Scalar Quantity, Vector Quantity, Reference Point, Kinematics, Uniform and Non Uniform Motion, Speed – Uniform and Non Uniform Speed, Average Speed, Speed Curve, Velocity , Acceleration, Retardation, Graphs, Formulas , etc

## Science Chapter 8 “Motion” Class 9 Study Notes

### Science Chapter 8 Class 9 Motion ( Study Notes )

1. SI Unit : International systems of derived units.

2. Motion : An object is said to be in motion if it changes its position with respect to time and a fixed reference point.

3. Rest : An object is said to be at rest if it does not changes its position with respect to time and reference point.

4. Distance : The total path length between two fixed points is called distance.
SI unit of Distance is metre (m).
➤ Distance is a Scalar Quantity.
➤ Distance can not be negative or zero.

5. Displacement : Displacement can be defined as the shortest distance between two fixed points along with the direction.
SI unit of Displacement is metre (m).
➤ Displacement is a vector Quantity
➤ If initial and final positions are same then, displacement is zero.

6. Scalar Quantity : A scalar quantity has only magnitude . Scalar quantity does not have direction.

7. Vector Quantity : A vector quantity has both direction and magnitude.

8. Reference Point : A fixed point with respect to which a body is at rest or in motion is known as reference point or origin.
➤ Rest and Motion are Relative terms

9. Kinematics : The branch of science that deals with the objects in motion is known as Kinematics. The word Kinematics means Motion.

10. Uniform Motion : An object is said to be in uniform motion if it changes its position equally in the equal time of intervals.

11. Non-Uniform Motions : An object is said to be in non-uniform motion if its position changes equally in unequally intervals of time or if its changes its positions unequally in equal interval of time.

12. Speed : Speed can be defined as the time rate of change in distance. Speed is denoted by ‘v’.
Mathematically,
Speed = Distance/time
v = s/t
SI Unit of Speed is m/s.
➤ Speed is a scalar quantity.
➤ Speed can not be negative.

13. Uniform Speed : An object is said to be moving with uniform speed if it changes its distance in equal interval of time.

14. Non-Uniform Speed : An object is said to be moving with non uniform speed if it changes its distance equally in unequal interval of time or it it changes its distance unequally in equal time intervals.

15. Average Speed (vav) : Average speed is defined as the ration of total distance travelled to the total time taken.
vav = (total distance)/(total time)
SI Unit of Average speed is m/s.

16. Velocity : The time rate of change of displacement is called velocity. It is denoted by ‘v’.
Mathematically,
v = displacement/time
SI Unit of Velocity is m/s.
➤ Velocity is a vector quantity
➤ Velocity can be positive or negative or zero.

17. Average Velocity : Average Velocity is defined as the mean of two velocities namely initial velocity (u) and final velocity (v).
Mathematically,
Average velocity = ( u + v ) / 2

18. Acceleration : The time rate of change of velocity is called acceleration. Acceleration is denoted by ‘a’ .
Mathematically,
Acceleration = (change in velocity) / (time taken)
a = (v-u) / t
SI unit of Acceleration is m/s2
➤ Acceleration is a vector quantity.
➤ Acceleration can be positive / negative/ zero.

19. Retardation (-a) : The negative value of acceleration is known as retardation or Deceleration.

20. Uniform Acceleration : if an object travels in a straight line and its velocity increases or decreases by equal amount in equal intervals of time, the the acceleration of the object is said to be uniform.

21. Non uniform Acceleration : An object can be travel with non uniform acceleration if its velocity changes at an non uniform rate.

22. Equations of Motion
➤ v = u + at [ First Equation of Motion – velocity – time relation ]
➤ s = ut + (1/2)at2 [ Second Equation of Motion – position – time relation ]
➤ v2-u2 = 2as [ Third Equation of Motion – position velocity relations ]

23. Uniform Circular Motion : If an object moves in a circular path with uniform speed, its motion is called uniform circular motion.

### Class 9 Motion Chapter 8 Graphs

1. Graphs : A graph depicts relation between two physical quantities as to show the dependence of one physical quantity with respect to another.

2. Position Time Graph

3. Distance Time Graph

4. Velocity time graph