What is Acceleration?

Acceleration is a change of an object's speed and velocity. Acceleration measures the amount of velocity and the direction as well, since velocity is a vector, also velocity is constant. Acceleration is never always increasing speed since gravity is an acceleration, which slows objects down. If a person were to throw a pencil in the air, the pencil will slow down and fall back down. If a car were to completely stop at a very steep hill after it speeds up the hill, the car would slow down and go back down. Another example is that if a ball rolls on a floor at a fast rate, it will still slow down due to gravity.