# Physics unit 2- motion

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## Distance time graphs/ velocity and acceleration

Help us describe the motion of an object
Speed of an object is distance travelled each second
If object stationary, line is horizontal
Constant speed =straight upwards slope
Speed(m/s)= distance travelled (m) divided by time taken (s)
Velocity is speed in a given direction
If changes direction, changes velocity. Even if same speed
If velocity changes, it accelerates.
Acceleration=final velocity minus initial velocity (m/s) divided by time taken for change (s)
If acceleration is negative, it's called deceleration
Acceleration is m/s squared

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## Velocity-time graphs

The gradient of a velocity-time graph represents acceleration
The steeper the gradient, the greater the acceleration
If line is horizontal, the acceleration is zero. Therefore the object is traveling at a steady speed
If the gradient of a line is negative, the object is decelerating

Calculating the area under the line between two times on a velocity-time graphs gives the distance travelled between those times.

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