P9: Motion

P9: Motion

1. Speed and distance-time graphs

   • Distance-time graphs can show us the speed a vehicle is travelling.
   • The gradient of the line tells us the speed of the car.
   • If the graph has a straight line, the speed is constant.
     • The steeper the gradient, the greater the speed.
   • If a graph has a curved line, then speed is changing.
     • Speed can be calculated at any point by working out the tangent to a point.
   • If the line is flat, then the vehicle has no speed and is not moving.

2. Velocity and acceleration

   • Velocity is speed in a given direction.
     • Two vehicles may have the same speed but different velocities dependant on their direction.
     • If a vehicle travels in a circular direction, its speed is the same however the velocity is continuously changing.
   • Displacement is the distance travelled in a given direction.
   • The acceleration of a vehicle is its change in velocity per second.
     • Deceleration is when a vehicle slows down.

3. Velocity-time graphs

   • The gradient of the line shows a vehicles' acceleration.
   • When brakes are applied to a vehicle, it begins to decelerate.
     • Because of this, the line of the graph will have a negative gradient.
   • The area under a velocity-time graph can calculate the distance travelled.

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