Welcome to Physics Welcome to Physics lesson…lesson…

FORCE AND MOTIONFORCE AND MOTION

Chapter 2

Prepared by Gayah Normahzura Bt Khaizan

Observe the animations Observe the animations below..below..

1

2

1

t = 0v = 0

v =

The car is….

t = 2 s

t

s = 0

s = 50 m

2

t

t = 0v = 30m/s

t = 3 sv = 0

The car is….

s = 0

s = 50 m

The objective of today’s The objective of today’s lesson is:lesson is:

Define acceleration and Define acceleration and deceleration and state that :deceleration and state that :

a = a = v – uv – u t

Previous Lesson..Previous Lesson..

Distance and displacementDistance and displacement Speed and velocitySpeed and velocity Average speed, Average speed,

Average velocity,Average velocity,

The SI unit for speed and velocity is __The SI unit for speed and velocity is ____.

v = ?

vv = ?

Previous Lesson..Previous Lesson..

Distance and displacementDistance and displacement Speed and velocitySpeed and velocity Average speed, Average speed,

Average velocity,Average velocity,

The SI unit for speed and velocity is m/s.The SI unit for speed and velocity is m/s.

v = s t

vv = s t

What will you learn now?What will you learn now?

Acceleration and decelerationAcceleration and deceleration

Definition

Equation

Activity…Activity…

Instruction..Instruction.. Discuss in groupDiscuss in group A car A car acceleratesaccelerates from rest to 15m/s in 15 s. from rest to 15m/s in 15 s. Plot a graph of velocity versus time with Plot a graph of velocity versus time with

given information.given information.

Time, t (s)Time, t (s) Velocity, v Velocity, v (m/s)(m/s)

0 0 00

55 55

1010 1010

1515 1515

Q1

Time, t Time, t (s)(s)

Velocity, Velocity, v (m/s)v (m/s)

0 0 00

55 55

1010 1010

1515 1515

Graph velocity versus time

0

2

4

6

8

10

12

14

16

0 5 10 15

t

v

v = 0

v = 15m/s

Time & Velocity changeTime, t increase

Velocity, v increase

m/s

(s)

DefinitionDefinition Acceleration Acceleration is defined as the is defined as the rate rate

of change of velocity.of change of velocity. The units for acceleration is m/s²The units for acceleration is m/s² EquationEquation

Acceleration= Acceleration= change of velocitychange of velocity time taken time taken

for the changefor the change a =a = v - u v - u

t t

Instruction..Instruction.. Discuss in groupDiscuss in group Plot a graph of velocity versus time with Plot a graph of velocity versus time with

given informationgiven information

Time, t (s)Time, t (s) Velocity, v Velocity, v (m/s)(m/s)

0 0 66

22 44

44 22

66 00

Q2

Graph velocity versus time

0

1

2

3

4

5

6

7

0 2 4 6

t

v

Time, t Time, t (s)(s)

Velocity, Velocity, v (m/s)v (m/s)

0 0 66

22 44

44 22

66 00

v = 6m/s

v = 0

m/s

(s)

a = v – u tv u

a

t

a acceleration

v

u

t

Final velocity

Initial velocity

Final velocity

EXERCISEEXERCISE

(1) An object moves from rest with a (1) An object moves from rest with a uniform acceleration of 2 msuniform acceleration of 2 ms-2 -2 .What .What is the velocity of the object after 30 is the velocity of the object after 30 s?s?

Answer…..Answer….. Solution…Solution… u = 0u = 0 t = 30 st = 30 s a = 2 msa = 2 ms-2-2

a = a = v- uv- u tt v = u + atv = u + at = o + (2 x 30)= o + (2 x 30) = = 60 ms60 ms-1-1

(2) A car increases its velocity (2) A car increases its velocity steadily from steadily from

72 km h72 km h-1 -1 to 108km hto 108km h-1-1 in 5 s. What in 5 s. What is its is its

acceleration in msacceleration in ms-2-2??

Answer……Answer…… Solution…..Solution….. u = 72km hu = 72km h-1-1 v = 108 km h v = 108 km h-1-1

= = 72 x 1 000 72 x 1 000 = = 108 x 1 000 108 x 1 000 m m ss-1-1

60 x 6060 x 60 60 x 60 60 x 60 = 20 m s= 20 m s-1-1 = 30 m s = 30 m s-1-1

t = 5 st = 5 sAcceleration, a = Acceleration, a = v – u v – u = = 30 - 2030 - 20 m m

ss-1-1

t 5t 5 = = 2 m s2 m s-2-2

m sm s-1-1