Linear motion and acceleration. Animation using the forward linear motion of a racing car to demonstrate the principles of speed (velocity) and acceleration. The counter across bottom indicates the time elapsed (in seconds), the distance covered (in metres), the speed (in metres per second) and the acceleration (in metres per second squared). Acceleration is the rate of change of velocity. Over the first six seconds, the car accelerates to a speed of 20 metres per second (72 kilometres per hour). It starts to accelerate again at 10 seconds, reaching a top speed of 45 metres per second (162 kilometres per hour). By the time 23 seconds have elapsed, it has covered a kilometre (1000 metres) and is braking sharply, decelerating. By the time the animation ends and the car recedes into the distance, it is moving at 15 metres per second (54 kilometres per hour).