# Physics - Motion - Chapter One

Distance - time graphs

Velocity and Acceleration

More about Velocity - Time Graphs

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• Created by: Courtney
• Created on: 04-05-11 17:26

## Distance - Time Graphs

We can use graphs to help us describe the motion of a body. A distant time graph shows the distance of a body from a starting point (y-axis) against time take (x-axis)

The slope of the line on a distance - time graph represents speed. The steeper the slope, the greater the speed.

The speed of a body is the distance travelled each second. We can calculate the speed of a body using the equation:

speed=distance travelled ÷  time taken

The unit of speed is metres per second (m/s).

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## Velocity and Acceleration

Velocity is the speed of an object in a given direction. If the body changes direction it changes velocity even if the speed stays the same.

• An object moving steadily round in a circle has a constant speed. Its direction of motion changes as it goes tound so its velocity is not constant.
• Two moving objects can have the same speed but different velocities. For example, a car travelling north at 30m/s on  a motorway has the same speed as a car travelling south at 30m/s. But their velocities are not the same because they are moving in opposite directions.

If the velocity of a body changes, we say that it accelerates. We can calculate acceleration using the equation :

acceleration = change in velocity  ÷ time taken for the change

The unit of acceleration is metres per second squared (m/s2).

If the value calculated for acceleration is negative, the body is decelerating - slowing down.

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## More about Velocity - Time Graphs

A velocity time graph shows the velocity of a body (y-axis) against time taken (x-axis).

Braking: This reduces the velocity of a vehicle. The velocity is constant until the driver applies the brakes.

• The slope of a line represents acceleration.
• The steeper slpoe, the greater the acceleration.
• If the slope is negative, the body is decelerating (slowing down)
• The area under the line represents the distance travelled in a given time.
• The bigger the area, the greater the distance travelled.
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Simple grammatical mistake (page 1):

'distant time graph'

'distance-time graph'

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Page 2 of 3:

'tound'