Acceleration is a measure of how fast velocity changes. Acceleration is the change of velocity divided by the change of time. Acceleration is a vector, and therefore includes both a size and a direction. An object was moving north at 10 meters per second. The object speeds up and now is moving north at 15 meters per second. The object has accelerated.
An apple is falling down. It starts falling at 0 meters per second. At the end of the first second, the apple is moving at 9.8 meters per second. The apple has accelerated. At the end of the second second, the apple is moving down at 19.6 meters per second. The apple has accelerated again.
Jane is walking east at 3 kilometers per hour. Jane's velocity does not change. Jane's acceleration is zero.
Tom was walking east at 3 kilometers per hour. Tom turns and walks south at 3 kilometers per hour. Tom has had a nonzero acceleration.
Sally was walking east at 3 kilometers per hour. Sally slows down. After, Sally walks east at 1.5 kilometers per hour. Sally has had a nonzero acceleration.

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