# Velocity

## Speed and direction of a motion / From Wikipedia, the free encyclopedia

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**Velocity** is the speed in combination with the direction of motion of an object. Velocity is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of bodies.

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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 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 is said to be undergoing an *acceleration*.