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Physics Motion Theory

Features of the Graph

1. The slope is the speed of the object.
2. If the slope is horizontal the object is not moving. a) run

To calculate the slope:

slope = rise run distance

To calculate the slope

slope = 8 – 6
2 – 1

run = 2 ms-1

Book A mop!, vjJs

Speed vsTime Graph
A change in the speed of an object is called acceleration. If the speed increases the object is accelerating, if it decreases then the object is decelerating. Acceleration is a measure of how
much an object’s speed changes each second. The units are: ms-2. Acceleration (a) can be
calculated by measuring the change in speed over a given time interval:

This means the acceleration equals the change in speed divided by the change in time.

Worked Example
Speed versus time graphs show how fast an object is moving.

Features of the Graph:
Speed versus Time Graph

The slope is the acceleration of the object.

If the slope is horizontal the object is moving at constant speed.

v) To calculate the slope:

acceleration = rise
= 10 – 0
5 – 0
= 10
= 2 ms-1

The area under a speed time graph is the distance travelled.
Area = 1/2. b . h
= 1/2 . 5 . 10
=25 m.