Reading Focus

Key Concepts

• How are changes in velocity described?

• How can you calculate acceleration?

• How does a speed-time graph indicate acceleration?

• What is instantaneous acceleration?

Vocabulary

• acceleration

• free fall

• constant acceleration

• linear graph

• nonlinear graph

Reading Strategy

Summarizing Read the section on acceleration. Then copy and complete the concept map below to organize what you know about acceleration.

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A basketball constantly changes velocity during a game. The player in Figure 11 dribbles the ball down the court, and the ball speeds up as it falls and slows down as it rises. As she passes the ball, it flies through the air and suddenly stops when a teammate catches it. The velocity of the ball increases again as it is thrown toward the basket.

But the rate at which velocity changes is also important. Imagine a basketball player running down the court and slowly coming to a stop. Now imagine the player running down the court and stopping suddenly. If the player stops slowly, his or her velocity changes slowly. If the player stops suddenly, his or her velocity changes quickly. The ball handler's teammates must position themselves to assist the drive or to take a pass. Opposing team members want to prevent the ball handler from reaching the basket. Each player must anticipate the ball handler's motion.

Figure 11 The basketball constantly changes velocity as it rises and falls.

Velocity changes frequently, not only in a basketball game, but throughout our physical world. Describing changes in velocity, and how fast they occur, is a necessary part of describing motion.