* An object at rest: A book sitting on a table isn't accelerating because its velocity isn't changing.

* An object moving at a constant speed in a straight line: A car driving at 60 mph on a straight highway isn't accelerating because both its speed and direction are constant.

* An object moving in a circle at a constant speed: While the object is changing direction, its speed is constant. Acceleration involves a change in speed *or* direction.

Key point: Acceleration means a change in velocity. Velocity is a combination of speed and direction.