Speeds

Speeds refer to how fast an object covers distance over time. In physics, speed is defined as the rate of motion and is computed as the distance traveled divided by the time taken. When speed is considered at a single moment, it is called instantaneous speed, which is the derivative of position with respect to time. The average speed over a given interval is the total distance divided by the total time.

Speed is a scalar quantity, meaning it has magnitude but no direction. The related concept of velocity combines speed with direction, and is a vector quantity. For example, a car might move at 60 kilometers per hour north, which specifies both magnitude and direction.

Common units include meters per second (m/s) and kilometers per hour (km/h); in some contexts miles per hour (mph) or knots are used. Conversions between units follow standard factors, and speeds can span many orders of magnitude, from the speed of light to everyday road speeds.

Measurement of speed relies on instruments and methods such as speedometers in vehicles, radar or lidar guns, GPS-based tracking, or timing devices. In fluids and gases, speeds may refer to flow rates or wind speeds; in acoustics, the speed of sound depends on the medium.

In physics, the speed of light in vacuum, c, is a fundamental constant, and no information or matter can travel faster in accordance with current theories. Actual speeds are constrained by forces, energy, and environmental conditions.

See also velocity, acceleration, and speed limits.