UNIT 7 Waves, Vibrations, and Sound

1. UNIT 7Waves, Vibrations,and Sound

2. ConcepTest 13.9 Grandfather Clock A grandfather clock has a weight at the bottom of the pendulum that can be moved up or down. If the clock is running slow, what should you do to adjust the time properly? 1) move the weight up 2) move the weight down 3) moving the weight will not matter 4) call the repair man

3. T = 2p (L/g) ConcepTest 13.9 Grandfather Clock A grandfather clock has a weight at the bottom of the pendulum that can be moved up or down. If the clock is running slow, what should you do to adjust the time properly? 1) move the weight up 2) move the weight down 3) moving the weight will not matter 4) call the repair man The period of the grandfather clock is too long, so we need to decrease the period (increase the frequency). To do this, the length must be decreased, so the adjustable weight should be moved up in order to shorten the pendulum length.

4. ConcepTest 13.10aPendulum in Elevator I A pendulum is suspended from the ceiling of an elevator. When the elevator is at rest, the period is T. What happens to the period when the elevator is moving upward at constant speed? 1) period will increase 2) period will not change 3) period will decrease

5. ConcepTest 13.10aPendulum in Elevator I A pendulum is suspended from the ceiling of an elevator. When the elevator is at rest, the period is T. What happens to the period when the elevator is moving upward at constant speed? 1) period will increase 2) period will not change 3) period will decrease Nothing at all changes when the elevator moves at constant speed. Neither the length nor the effective value of g has changed, so the period of the pendulum is the same.

6. ConcepTest 13.10bPendulum in Elevator II A pendulum is suspended from the ceiling of an elevator. When the elevator is at rest, the period is T. What happens to the period when the elevator is accelerating upward? 1) period will increase 2) period will not change 3) period will decrease

7. ConcepTest 13.10bPendulum in Elevator II A pendulum is suspended from the ceiling of an elevator. When the elevator is at rest, the period is T. What happens to the period when the elevator is accelerating upward? 1) period will increase 2) period will not change 3) period will decrease When the elevator accelerates upward, the hanging mass feels “heavier” – this means that the effective value of g has increased due to the acceleration of the elevator. Since the period depends inversely on g, and the effective value of g increased, then the period of the pendulum will decrease (i.e., its frequency will increase and it will swing faster).

8. Thursday January 26th WAVES, VIBRATIONS, AND SOUND

9. TODAY’S AGENDA Thursday, January 26 • Wave Properties • Hw: Practice D (All) p387 UPCOMING… • Thur: Properties of Waves • Problem Quiz #1 • Fri: Wave Interactions • Mon: Sound Waves

10. Chapter 11 Vibrations and Waves

11. Units of Chapter 11 • Forced Vibrations; Resonance • Wave Motion • Types of Waves: Transverse and Longitudinal

12. Wave Motion A wave travels along its medium, but the individual particles just move up and down.

13. Wave Motion All types of traveling waves transport energy. Study of a single wave pulse shows that it is begun with a vibration and transmitted through internal forces in the medium. Continuous waves start with vibrations too. If the vibration is SHM, then the wave will be sinusoidal.

14. Wave Motion • Wave characteristics: • Amplitude, A • Wavelength, λ • Frequency f and period T • Wave velocity (11-12)

15. Types of Waves: Transverse and Longitudinal The motion of particles in a wave can either be perpendicular to the wave direction (transverse) or parallel to it (longitudinal).

16. Types of Waves: Transverse and Longitudinal Sound waves are longitudinal waves:

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