What is the difference between speed and acceleration?

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gsenviro | College Teacher | (Level 1) Educator Emeritus

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Speed is given as a ratio of distance travelled over time and is a scalar quantity, that is, it has only magnitude and no direction. Which means that irrespective of whether the object rotates around a fixed point or moves away from it in a straight line, it can have the same speed, provided it travelled the same distance in same time. Velocity is a vector quantity that denotes the displacement of an object per unit time. It has both a magnitude and a direction. Comparing with the speed, velocity can be zero even if the object has travelled some distance (that is has a non-zero velocity), if the displacement is zero. The rotation around a fixed center is a good example of this scenario. Both, the velocity and speed have units of length over time, that is, meter per second or km per hour. 

Acceleration is the rate of change of velocity and has units of length per time squared, that is, meter per second squared or km per hour squared. The most common example of acceleration is acceleration due to gravity (g), which ensures that all the objects falling down accelerate at the same value. Also, acceleration is a vector quantity unlike speed (which is scalar).

Hope this helps.