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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More about velocity-time graphs

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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