This overhead view of an animated car illustrates its velocity and acceleration as it starts up, moves in a straight line, and turns. Velocity is one way we describe motion, and includes the notions of both speed and direction: going fast versus going slow, going east versus going north. Velocity is how position changes with time. Acceleration is how we describe the changes in velocity over time: speeding up, slowing down and changing direction are all examples of when acceleration occurs.