We humans are in continuous motion. At home, we frequently move from one area of the house to the other. We often travel to school, shops, playing grounds and other areas of interest by walking or cycling or by taking the bus, taxi or using the family car. In all instances, we travel a certain distance in a certain amount of time. If the shop is close to our home, we can walk to the shop in a given amount of time. If we walk faster to the same shop, it will take us less time. Running or cycling to the shop will take even less time. The amount of time that we take to travel a given distance depends on the speed at which we travel.

The speed of a moving object relates the distance travelled by the object to the time taken to travel this distance. We can express this in the form of a mathematical equation:

            Distance

Speed = time

Scientists prefer to use symbols to express quantities, such as distance, speed and time. The scientific symbol for speed is v, the symbol for distance is s and t is the symbol for time, We can therefore write the equation

V= s/t

The unit for speed is the unit for distance (which is the metre) divided by the unit for time (which is the second).

So, the unit for speed is which can also be written as m/s or as ms-1. Another unit of speed commonly used, especially in everyday travel, is km/h. A car travelling at a speed of 50 km/h will travel 50 km in 1 hour. Remember that speed in motor cars is measured by a