Speed

Speed is a physical quantity that describes how fast an object moves. It is calculated by dividing the distance travelled by the time taken and is measured in metres per second (m/s) in the International System of Units (SI). In everyday life, speeds are also commonly expressed in kilometres per hour (km/h) or miles per hour (mph).

A higher speed means that an object covers a greater distance in the same amount of time. Speed is different from velocity, which includes both the rate of motion and the direction of travel. For example, two cars can move at the same speed while travelling in opposite directions, so their velocities are different.

Speed is used in many areas of science, engineering and everyday life. Drivers rely on speedometers to monitor how fast they are travelling, while scientists use precise instruments to measure the speed of everything from tiny particles to distant galaxies. Different objects can move at vastly different speeds.

Sound travels through dry air at about 343 metres per second at 20 °C, whereas light moves through a vacuum at about 299,792 kilometres per second, the highest speed known in nature. Understanding speed helps explain motion, calculate travel times and design safer vehicles, transport systems and machines. It is one of the fundamental concepts used to describe how objects move and interact in the physical world.