The Open Door Web Site : Physical Science : Mechanics : Speed and Acceleration : Speed or Velocity

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Physics Section A : Speed and Acceleration

Part 1: Information

Speed or Velocity ?

The speed of an object is a scalar quantity, which means that it has size only.

The velocity of an object is a vector quantity, which means that it has size and direction.

Look at these diagrams :

A and B represent the routes taken by two cars travelling at 60 km/h. Since car A is constantly changing its direction, we should refer to its speed. Since car B is travelling in one direction, we should refer to its velocity.

N.B Speed and velocity are measured in the same units.