Take your students on an amusement park ride—for just a penny! Discuss how an object can be accelerating yet moving at
constant speed. Investigate how a change in direction (at constant speed) is acceleration; that is, centripetal acceleration!
Velocity is the rate of motion in a specified direction and acceleration is a change in an object’s velocity. Both velocity and acceleration are vector quantities in that they are based on a magnitude AND a specified direction (i.e., the car is traveling north at 55 mph). Speed, on the other hand, is an object’s rate of motion. Speed is a scalar quantity and is based only on a magnitude (i.e., the car is traveling at 55 mph). Whenever there is a force, there is acceleration according to Newton’s second law of motion (F = ma). A force is required to change an object’s speed, and a force is required to change an object’s direction. Since velocity is a quantity of speed and direction, a change in an object’s speed OR a change in its direction, or both cause the object to accelerate. The force can change the speed of the object without affecting its direction (linear acceleration), or the force can change the direction of the object with or without affecting its speed (centripetal acceleration).