REVIEW VOCABULARY

average velocity

NEW VOCABULARY

Student Edition, pp. 160–161

MAIN IDEAWrite the Main Idea for this section.

Recall and write the definition of the Review Vocabulary term.

average velocity

Use your book to fill in the term that matches each definition.

the movement of an object at a constant speed around a circle with a fixed radius

the acceleration of an object in uniform circular motion

the net force toward the center of the circle acting on an object moving in a circle

Write the equation for centripetal acceleration and extend it to include the variable for the period, T. Then, describe what each term means.

6 Motion in Two Dimensions2 Circular Motion

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Student Edition, pp. 162–163

Use with Example Problem 3.

Use this column for

scratch work and

sketches.

2 Circular Motion (continued)

TRY IT!

Problem

UNIFORM CIRCULAR MOTION A 35-g rubber ball is attached to a 1.32-m string. The ball is swung in a horizontal circle, making one revolution in 1.15 s. Find the magnitude of the tension force exerted by the string on the rubber ball.

1. ANALYZE AND SKETCH THE PROBLEM

KNOWNS UNKNOWNS

m =  r =   = ?

T = 

2. SOLVE FOR THE UNKNOWNS

Find the magnitude of the centripetal acceleration.

Use Newton’s second law to find the magnitude of the tension in the string.

3. EVALUATE THE ANSWER

• Are the units correct?

Summarize the main idea about centrifugal “force.”

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SUMMARIZE

How does the MAINIDEA for this section relate to the chapter’s BIGIDEA?

REVIEW IT !

17. MAINIDEA If you attach a ball to a rope and swing it at a constant speed in a circle above your head, the ball is in uniform circular motion. In which direction does it accelerate? What force causes the acceleration?

18. Uniform Circular Motion What is the direction of the force that acts on the clothes in the spin cycle of a top-load washing machine? What exerts the force?

19. Centripetal Acceleration A newspaper article states that when turning a corner, a driver must be careful to balance the centripetal and centrifugal forces to keep from skidding. Write a letter to the editor that describes physics errors in this article.

20. Free-Body Diagram You are sitting in the back seat of a car going around a curve to the right. Sketch motion and free-body diagrams to answer these questions:

2 Circular Motion (continued)

a. What is the direction of your acceleration?

b. What is the direction of the net force on you?

c. What exerts this force?

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21. Centripetal Acceleration An object swings in a horizontal circle, supported by a 1.8-m string. It completes a revolution in 2.2 s. What is the object's centripetal acceleration?

22. Centripetal Force The 40.0-g stone in Figure 13 is whirled horizontally at a speed of 2.2 m/s. What is the tension in the string?

23. Amusement-Park Ride A ride at an amusement park has people stand around a 4.0-m radius circle with their backs to a wall. The ride then spins them with a 1.7 s period of revolution. What are the centripetal acceleration and velocity of the riders?

24. Centripetal Force A bowling ball has a mass of 7.3 kg. What force must you exert to move it at a speed of 2.5 m/s around a circle with a radius of 0.75 m?

25. Critical Thinking Because of Earth’s daily rotation, you always move with uniform circular motion. What is the agent that supplies the force that causes your centripetal acceleration? If you are standing on a scale, how does the circular motion affect the scale’s measure of your weight?

2 Circular Motion (continued)

0.60 m

Figure 13

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