Figure 13 When you ride on a carousel, you accelerate because of the changing direction.

Changes in Direction Acceleration isn't always the result of changes in speed. You can accelerate even if your speed is constant. You experience this type of acceleration if you ride a bicycle around a curve. Although you may have a constant speed, your change in direction means you are accelerating. You also may have experienced this type of acceleration if you have ridden on a carousel like the one in Figure 13. A horse on the carousel is traveling at a constant speed, but it is accelerating because its direction is constantly changing.

Changes in Speed and Direction Sometimes motion is characterized by changes in both speed and direction at the same time. You experience this type of motion if you ride on a roller coaster like the one in Figure 14. The roller coaster ride starts out slowly as the cars travel up the steeply inclined rails. The cars reach the top of the incline. Suddenly they plummet toward the ground and then whip around a curve. You are thrown backward, forward, and sideways as your velocity increases, decreases, and changes direction. Your acceleration is constantly changing because of changes in the speed and direction of the cars of the roller coaster.

Similarly, passengers in a car moving at the posted speed limit along a winding road experience rapidly changing acceleration. The car may enter a long curve at the same time that it slows to maintain a safe interval behind another car. The car is accelerating both because it is changing direction and because its speed is decreasing.

Figure 14 A roller coaster produces acceleration due to changes in both speed and direction. Applying Concepts Describe the acceleration occuring at this instant on the rollercoaster ride.

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