1. Unit 4 - Acceleration
Science for 7th Grade

2. Module Objectives
To know about uniform and non uniform motion.
To learn about acceleration and its types.
Acceleration in day to day life
Numerical Activity

3. Introduction
When an object moves with constant speed and direction ,we say it moves in uniform motion
If it changes its speed and direction at regular intervals of time it is said to be in non uniform motion.
Non Uniform motion is also called Acceleration.

4. What is Acceleration? Speed is the rate of change of position
Acceleration is the rate of change of velocity.
Can be an:
Increase in speed
Decrease in speed
Change in direction
If a body moves with uniform velocity its acceleration
Is zero ms-2 . Why?

5. Speeding Up or Slowing Down?
When a car speeds up,
that is
POSITIVE ACCELERATION!
When a car slows down,
NEGATIVE ACCELERATION
or DECELERATION !

6. Acceleration Formula Acceleration = Change in Velocity/Time
a=(Final Velocity-Initial Velocity)/Time
a=(Vf-Vi)/t

7. Positive Acceleration
A motorcycle starts at rest and accelerates to 80 m/s in 20 seconds
a=(Vf-Vi)/t = (80 m/s – 0 m/s) / 20s
a= 4 m/s2

8. Positive Acceleration Graph

9. Negative Acceleration/Deceleration
A skateboarder moves in a straight line at 3 m/s and comes to a stop in 2 s.
a=(Vf-Vi)/t = (0 m/s – 3 m/s)/2s
a = m/s2
All non accelerated motions are not decelerated
Motion .Why?

10. Deceleration Graph

11. Acceleration Everywhere
Car moving in a curved path
Elevator going up
Rocket launching

12. Solved Numericals
Find the acceleration gained by the a body in 5 seconds if its initial velocity is 20m/s and final velocity is 40 m/s?

13. Solved Numericals
A motor cyclist moving with certain velocity comes to rest in 6 seconds .Calculate the initial velocity if he was decelerated by -3 ms -2?

14. Unsolved Numericals
If a body moves with uniform velocity then its acceleration is ?
a)uniform b)non uniform
c) zero d)negative
Acceleration of a body is the rate of change of ?
a) distance travelled b) speed
c) displacement d) velocity

15. Unsolved Numericals
The acceleration of a body is 3ms -2 .This means that velocity changes by in every two seconds by ?
a)2 ms b) 3 ms-1
c) 6 ms d) 9 ms-1
A physical quantity having magnitude and direction is ?
a) time b) acceleration
c) speed d) distance travelled

16. Fill In The Blanks The S.I. Unit of Acceleration is _____________.
The negative acceleration is _____________.
If a moving body comes to a stop ,its final velocity is _______.
The velocity gained in 5 seconds by a body moving with uniform acceleration of 1 ms -2 is _____________.
A scalar quantity has only _____________.

17. Match The Following

18. Answer The Following
State the difference between uniform and nonuniform motion.
Define acceleration with an example.
Distinguish between acceleration and deceleration.
What is meant by uniform acceleration? State its S.I. Unit.
Explain the term deceleration with an example.
Calculate the acceleration of a body if it starts from rest and attains the velocity 20 m/s in 10 seconds.

19. Numericals
An object moving at a velocity of 24m/s is brought to a halt in 8 seconds by applying a force in opposite direction to the motion .Calculate the acceleration?
If a vehicle is accelerated to 5m/s -2. how much time does it take to attain a velocity of 27 m/s which initially starts with 2m/s?
What does it imply and why? If:
a) acceleration of a body is zero ms -2
b) initial velocity of a body is ms -1
c)final velocity of a body is zero ms -1

20. Give Reasons
A car is travelling on an uneven mud road is an example of non-uniform motion?
Acceleration and deceleration have the same unit units yet they have difference