Speed

Speed is a rate of progress. It is a measure of how fast or slow an object is moving. Because speed may vary over the duration of a journey, we use average speed to simplify calculations. Average speed is calculated by distance over time. The S.I. unit of length is metre (m) while the S.I. unit of time is seconds (s). Hence, the S.I. unit of speed is metre per second (m/s). Other common units are centimetre per scond (cm/s) and kilometres per hour (km/h).