The speed of an object tells how fast it is moving. Speed is a scalar quantity, which is defined as the rate of distance traveled. A moving object may not always maintain a constant fastness, rather it varies with time. Therefore, we define average speed.

Average speed, v, is defined as the total distance traveled, s, divide by the total time, t, taken to cover the distance. The mathematical form of this definition is given by

The SI unit of time is second (s), the SI unit of distance is meter (m) and hence the SI unit of speed becomes metersper second (m/s). Other non-SI units of speed are kilometers per hour (km/h), miles per hour (mph), etc.