speed

Speed is the magnitude of the rate at which an object covers distance. In physics, speed is a scalar quantity, meaning it has only magnitude and no directional component. It describes how fast an object moves and is commonly expressed in meters per second (m/s), kilometers per hour (km/h), or miles per hour (mph). Speed is related to velocity, which includes both speed and direction.

Average speed equals total distance traveled divided by the total time taken. Instantaneous speed is the speed at a specific moment, formally the limit of distance over time as the interval approaches zero. An object may have changing speed and direction; uniform motion has constant speed, while nonuniform motion features changing speed. Angular speed describes how quickly an object rotates, measured in radians per second (rad/s).

The universal speed limit is the speed of light in vacuum, about 299,792,458 meters per second (c). In practice, no object with mass can reach or exceed c due to relativistic effects. Everyday speeds are affected by forces such as gravity, friction, and air resistance, and are studied within contexts ranging from sports to engineering.

Measurement methods include vehicle speedometers, radar and lidar devices, timing gates, and GPS-based calculations. Speed is a fundamental concept in motion analysis, with wide applications in transportation, safety, science, and everyday life.