simply. speed. Rate at which an object’s position changes in a specific direction over time. A vector quantity. See acceleration and vector.
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As a change of direction occurs while the racing cars turn on the curved track, their velocity is not constant.
The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of its speed and direction of motion (e.g. to the north). Velocity is an important concept in 60 km/hkinematics, the branch of classical mechanics that describes the motion of bodies.
Velocity is a physical vector quantity; both magnitude and direction are needed to define it. The scalar absolute value (magnitude) of velocity is called "speed", being a coherent derived unit whose quantity is measured in the SI (metric) system as metres per second (m/s) or as the SI base unit of (m⋅s−1). For example, "5 metres per second" is a scalar, whereas "5 metres per second east" is a vector.
If there is a change in speed, direction or both, then the object has a changing velocity and is said to be undergoing an acceleration.