Chapter 4 making sense of the universe. How do we describe motion? y terms used to describe motion in science velocity, acceleration, and momentum. Speed, velocity, and acceleration y the speed of the car tells us how far it will go in a certain amount of time. 100 kilometers per hour going due north describes a velocity y the car has an acceleration if its velocity is changing in any way, whether in y speed or direction or both. For example, as you speed up in a car you feel yourself being pushed back into your seat. As you slow down you feel yourself being pulled forward from the seat. As you drive around a curve you feel yourself being pushed away from the direction of your turn. In contrast, you don t feel such effects when moving at constant velocity.