It is not only moving objects whose speed can vary. The speed of the wind and the speed of sound also vary. A typical value for the speed of sound in air is about 330 m/s.

Velocity-time graphs show velocity on the vertical axis. Acceleration is still represented by the gradient. Key fact The gradient of speed-time and velocity-time graphs represent acceleration.

The phase and the group velocity of light propagating in conventional optical media cannot exceed the speed of light in ...