# Motion

## Speed and distance-time graphs

Speed distance moved per unit of time -scalar quanity

The speed of an object is s=v*t

distance travelled,m=speed,m/s*time taken,s

The distance-time graph for any object that is:

• stationary, is a horizontal line
• moving at a constant speed, is a straight line that slopes upwardd

The gradient of a distance-time graph represents the objects speed

When an object is accelerating, you can find its speed at any given point by drawing a tangent to the graph and working out the gradient of the gradient

Typical everyday speeds in m/s

walking 1.5,  running 3,  cycling,  6,  cyclist 6,  cars 31,  sound waves 330,  light waves 3x108

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## Velocity and acceleration

Velcocity speed at a given time -vector quanity

Acceleration change of velocity per second when an object slows down -vector quanity

The acceleration of an object is q=v-u/t

acceleration,m/s"2=change in velcoity,m/s/time taken for the change,t

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The gradient of the line on a velocity-time graph represents acceleration

Interpreting velocity-time graphs

• Horizonal line, object is travelling at constant velcoity, the gradient is zero so acceleration is zero
• sloping line upwards, the object is accelerating
• sloping line downwards, the object is accelerating
• The area under the graph tells us the distance travelled
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## Analyzing motion graphs

Gradient of the line height of the triangle/the base of the triangle

V"2-U"2=2as

change in velocity= 2*acceleration*distance travelled

This equation is useful for calculations where time is not given and the acceleration is constant

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