Motion in Physics

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Class: 09 Subject - Science
MOTION - 4

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3. Class 09
Subject Science
Chapter 8, Motion
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To study more log on to: www.geneo.in
Recommended Learning
Chapter : 8
Textbook Page Number : 98-113
Video : Motion in a straight line, Introduction to Motion, Distance and
Displacement, Motion- uniform and Non-Uniform, Measuring the rate of
motion, Speed with direction, Speed and its application, What is velocity,
Calculating average velocity and speed, Acceleration and its types

5. Summary
POINTS FOR
DISCUSSION
Recapitulation
Velocity- Time Graphs
Equations of Motion by Graphical Method
Circular Motion
Q & A

6. Objectives
1
Recapitulation
Fill in the blanks:
• Motions are of two types …………….and ………………….
• Formula of speed is…………………..
• Average speed is equal to ………………….
• Velocity is equal to …………………
• Average velocity for an object at a uniform rate of motion is
……………..

7. Objectives
2
Recapitulation
Acceleration
Uniform Non-Uniform
Motion
Uniform Non-Uniform

8. 3
Recapitulation
Distance Time Graphs
2. Non - Uniform Motion
Nonlinear variation in distance
travelled by the object with respect to
equal time interval.

9. Objectives
4
Practice Problem
Q. If the displacement of an object is proportional to the square of time,
then the object moves with
Uniform Velocity
Increasing acceleration Decreasing acceleration
Uniform Acceleration
A B
C D

10. Objectives
5
Practice Problem
Q. From the given υ – t graph, it can be inferred that the object is
In Uniform Motion
In Non-Uniform Motion
Moving with uniform
acceleration
At rest
A B
C D

11. 6
Graphical Representation of Motion
Velocity Time Graphs
1. Uniform Velocity To Calculate Distance
• AB denotes (t2 – t1) the time interval
• AC or BD denote velocity
(v2 – v1) = 40 Km/h
• Distance s covered by the
object in (t2 – t1) is ,
• D = AC × CD
• D = ( 40 km/h × (4 – 1 h)
• D = 40 X (3) km = 120 Km
• Area of the rectangle of ABCD
The variation in velocity with time for an object moving in a straight line can
be represented by a velocity-time graph

12. 7
Graphical Representation of Motion
Velocity Time Graphs
2. Uniform Acceleration
• The nature of the graph shows that
velocity changes by equal amount in
equal intervals of time.
• Thus, for all uniformly accelerated
motion, the velocity-time graph is a
straight line.

13. 8
Graphical Representation of Motion
Velocity Time Graphs
2. Non-Uniform Acceleration
• The nature of the graph shows that
velocity changes by unequal amount
in equal intervals of time.

14. Objectives
9
Practice Problem
Q. Velocity-time graph of an object is given below. The object has
Uniform velocity
Uniform retardation Variable acceleration
Uniform speed
A B
C D

15. 10
Equations Of Motion By Graphical Method
There are 3 equations of motions :
1. v = u +at
2. s = ut + ½ at2
3. 2as = v2
-u2
Where,
u – Initial Velocity of the Object
v – Final Velocity of the Object
a – Acceleration
t – time interval

16. 11
Equation For Velocity - Time Relation
1. v = u + at
The above equation represents
Velocity time relation.
Consider the body moving under
uniform acceleration,
Initial Velocity = u m/s2
Final Velocity = v m/s2
Time = t secs
The velocity changes at a uniform
rate a m/s2.
Initial Velocity is represented as OA and Final Velocity by BC and time
interval t is represented as OC.
BD = BC- CD Represents the change in velocity in time interval t.
🡪
Let us draw AD parallel to OC

17. 12
Equation For Velocity - Time Relation

18. 13
Equations For Position - Time Relation
• Let us consider that the object has travelled
a distance s in time t under uniform
acceleration a.
• The distance travelled by the object is
obtained by the area enclosed within OABC
under the velocity-time graph AB.
• The distance s travelled by the object is
given by:

19. 14
Equations For Position - Velocity Relation
Let us consider that the object has travelled a distance s in time t
under uniform acceleration, a is given by the area enclosed within the
trapezium OABC in the graph

20. Objectives
15
Practice Problem [NCERT-Exemplar]
Q. Area under a v – t graph represents a physical quantity which has the
unit
m
m3 m.s-1
m2
A B
C D

21. Objectives
16
Practice Problem
Q. Four cars A, B, C and D are moving on a levelled road. Their distance
versus time graphs are shown in the adjacent figure. Choose the correct
statement.
Car A is faster than car D.
Car D is faster than car C. Car C is the slowest
Car B is the slowest.
A B
C D

22. Objectives
17
Practice Problem [NCERT-Exemplar]
Q. An object starting from rest travels 20 m in first 2 s and 160 m in next 4
s. What will be the velocity after 7 s from the start.

23. 18
Circular Motion
CIRCULAR MOTION
• A body is said to be in Circular motion when it moves around
a fixed point in a closed path.
UNIFORM CIRCULAR MOTION
When a body is moving in a circle at a constant speed.

24. 19
Uniform Circular Motion
r

25. 20
UNIFORM CIRCULAR MOTION
When a body is moving in a circle at a constant speed it is
said to be in uniform circular motion.
But is the body in uniform circular motion moving at a
constant velocity?
r
Tangential
velocity
Uniform Circular Motion

26. 21
UNIFORM CIRCULAR MOTION
A body moving in a circle at a constant speed but changing velocity,
but is there any acceleration here?
r
v
Acceleration = Rate of change in velocity
Uniform Circular Motion

27. 22
What is the direction of acceleration?
There is some force acting on the ball and it acts inwards and it is
called as centripetal force. It keeps the ball in circular motion.
r
v F
a
Uniform Circular Motion

28. 23
r
v F
a
Uniform Circular Motion

29. Objectives
24
Practice Problem
Q. Suppose a person is moving on a circular path with a constant speed of
20 m.s-1
it implies that the person is
At rest
In accelerated motion Moving with uniform velocity
Moving with no acceleration
A B
C D

30. 25
• The motion of an object moving at uniform acceleration can be described
with the help of the following equations, namely
v = u + at
s = ut + ½ at2
2as = v2
– u2
where u is initial velocity of the object, which moves with uniform
acceleration a for time t, v is its final velocity and s is the distance it
travelled in time t.
• If an object moves in a circular path with uniform speed, its motion is
called uniform circular motion.
SUMMARY

31. Question
Answer
Time

32. LEARN
SESSION
To study more log on to: www.geneo.in
Recommended Learning
Chapter : 8
Textbook Page Number : 98-113
Video : Motion in a straight line, Introduction to Motion, Distance and
Displacement, Motion- uniform and Non-Uniform, Measuring the rate of
motion, Speed with direction, Speed and its application, What is velocity,
Calculating average velocity and speed, Acceleration and its types

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