Speed is a scalar quantity that measures how fast an object moves, defined as the rate at which an object changes its position over time. It is calculated by dividing the distance traveled by the time taken:
Speed=Distance/Time
The SI unit for speed is meters per second (m/s), but in everyday usage, kilometers per hour (km/h) and miles per hour (mph) are also common.
Speed differs from velocity; while speed refers only to how fast an object is moving, velocity also includes the direction of motion.
In various contexts, “speed” can also refer to the rate at which something happens or is done, such as the speed of a process or the speed at which information is transmitted.
Additionally, “speed” has informal uses, such as a colloquial term for methamphetamine.