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Definition: Distance travelled per unit time. Speed is the scalar quantity that is the magnitude of the velocity vector.

The most common way to calculate the constant velocity of an object moving in a straight line is with the formula:

r = d / t


  • r is the rate, or speed (sometimes denoted as v, for velocity, as in this kinematics article)
  • d is the distance moved
  • t is the time it takes to complete the movement

The SI units for speed are m / s (meters per second).

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