LESSON 2 -MOTION

1. Speed and velocity

2. Learning objectives
Students will be able to
• Define speed
• Define velocity
• Calculate speed and velocity

3. WARM UP

4. Speed
• Distance moved per second or rate of
change of distance
• It is scalar quantity
• Unit-m/s
• Average speed=Distance travelled/time
taken

5. Velocity
• Velocity measures rate of change of
displacement
• Average velocity=Displacement/time taken
• It is a vector quantity.
• Unit- m/s

6. CONTINOUS ASSESSMENT
1.What does the speedometer of a car measure?
2.A car travels a distance of 2oom and returns to the
original position after 5min.What is the speed and
velocity of the car?
3.What is the eqn. for speed?
4.What is the eqn. for time taken?

8. Final assessment
1.a)Define speed
b) Define velocity
(page42)

9. HOME WORK
• Page.33
Example.2

10. GRAPHS
Displacement –time graph
a) Body at rest
t
S
t(s) 0 1 2 3 4
S(m) 2 2 2 2 2

11. b)Body moving with steady velocity
t
s
t(s) 0 1 2 3 4
S(m) 0 5 10 15 20
Displacement
Gradient=
Time
Gradient of displacement –time graph gives
velocity. Steeper the line ,larger the velocity.

12. c)Accelerating body
t 0 1s 2s 3s 4s
s 0m 1m 4m 9m 16
a=2m/s²
t
s
Gradient at different time instants are different, as the
velocity is changing at every instant.
Gradient at any instant gives the instantaneous
velocity

13. d)Decelerating body
t
s

14. Velocity –time graph
a) Body moving with steady velocity
t
v

15. b)Body moving with steady acceleration
t
v
t(s) 0 1 2 3 4
v(m/s) 0 5 10 15 20
acceleration
Changeinvelocity
• Gradient=
Time
• Gradient of velocity –time graph gives
acceleration.
• Steeper the line ,larger the acceleration.


16. c)Body moving with steady deceleration
t
v
t(s) 0 1 2 3 4
v(m/s) 20 15 10 5 0
Changeinvelocity
• Gradient=
• Gradient of velocity –time graph gives
acceleration.
• Steeper the line ,larger the deceleration.
acceleration deceleration
Time
 /

17. Area under the velocity –Time graph gives the
displacement
Calculate the total displacement of
the given body using the given
velocity time graph.

18. OA-accelerated motion; Displacement = 100m
AB-Steady velocity ; Displacement = 400m
BC—decelerated motion; Displacement = 50m
Total displacement = 100+400+50=550m

19. Page43. Qn . 8

20. a) acceleration= gradient of OA
=change on y/change on x
=y2-y1/X2-X1 =2-0/3-0
=2/3 =1.5m/s²
b) Decelerates, its velocity becomes zero and it
reaches the maximum height.
c)At point C the velocity of the lift is zero. The
height=Displacement=area under OABC
= ½ × 3 × 2 + 6 × 2 + ½ × 3 × 2
=3+12+3=18m.
d)The lift starts moving down. First it accelerates in
the downward direction.Then it starts decelerating
and come to rest e) 18-6=12m

21. PAGE 106

23. • Home Work
• Page 106 Qn.no.25a

24. Horizontally Launched Projectiles
Imagine a cannonball being launched from a
cannon atop a very high cliff. What will be the
path of the cannonball and how can the motion
of the cannonball be described?

25. PROJECTILE
• A projectile is an object upon which the
only force is gravity.
• Gravity, being a downward force, causes
a projectile to accelerate in the
downward direction.
• The force of gravity could never alter the
horizontal velocity of an object .A vertical
force does not effect a horizontal motion.

26. COMPONENTS OF A VECTOR
• These two parts of the two-dimensional vector are
referred to as components.
• A component describes the effect of a single vector
in a given direction. Any force vector that is exerted
at an angle to the horizontal can be considered as
having two parts or components.
• The vector sum of these two components is always
equal to the force at the given angle. This is
depicted in the diagram below.

27. COMPONENTS OF VECTORS
A ACos

x

A ASin

y

A
x
A  x

32. http://www.physicsclassroom.com/Cl
ass/vectors/u3l2a.cfm