Motion Graphs

1. Speed .

. )(

)()(

Time

DistanceSpeed m or cm/second

m or cm

seconds S

D

T

Examples using the Speed Formula (Showing full working):

1. The sprinter ran 100 metres in 10 seconds. What was his speed ?

Time

DistanceSpeed

s

m

10

100 sm /10

2. The porsche travelled at 40 m/s for 2 minutes. How far did it go ?

TimeSpeedDistance ssm 120/40 m4800

Nb VELOCITY (v)is simply speed in a given directionDISPLACEMENT (S) is the distance in a given direction

2. Acceleration

The acceleration of something tells us how quickly its speed is changing.We can say that acceleration is the amount ………..changes per …….…...speed second

)(

)()(

Time

SpeedinChangeonAccelerati metres/second 2

metres/second

secondsA

S

T

Time

SpeedinChangeonAccelerati

t

uv

1. The ferrari was travelling at 20 m/s behind a lorry. It pulled out to overtake and accelerated at 4 m/s2 for 2 seconds. What was its new speed ?

TimeonAcceleratispeedinChange ssm 2/4 2 sm /8

New Speed = Old Speed + Change in Speed = 20 m/s + 8 m/s = 28 m/s

or Where v = final velocity

u = initial velocity

4. Motion Represented on Graphs.

There are two types of motion graphs, and three types of motion. Best represented in a table.

Velocity/TimeDistance/Time

Stopped

Const’ Velocity

Const’ Accel’n

D

t

D

t

D

t

V

t

V

t

V

t

Gradient = Velocity Gradient = Accel’nArea = Distance

travelled

Question

Velocity Time Graph for parachutist.

150

15

15

50 100

V (m/s)

T (s)

A. What was his acceleration from 0 to 15 sec ?

T

VA

s

sm

15

/150

2/10 sm

B. What was happening at 50 seconds?

He had just opened his parachute and was decelerating.

C. Approximately how far did he fall altogether?

Area under graph 50 150 + 50 15 = 8250m

Distance time graphs ;Summary The gradient of a distance time

graph gives the velocity increasing gradient means object

is accelerating decreasing gradient means object

is decelerating zero gradient means object is

stationary

Velocity time graphs; Summary

The gradient of a velocity time graph gives the acceleration of an object

the area under a velocity time graph gives the total distance traveled

Increasing or decreasing gradient gives the rate at which the acceleration is increasing or decreasing

Zero gradient means the object is travelling at constant speed

Problems

1. Calculate the speed over OA AB and BC

2. Calculate (a)the acceleration over OA, AB and BC

(b) the total distance traveled in the 12 s

5, 0, 3.75m

5m/s2, 0, 3.75m/s2, 127.5m