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### Wednesday January 25th

ConcepTest 13.2 Speed and Acceleration

1) x = A

2) x > 0 but x < A

3) x = 0

4) x < 0

5) none of the above

A mass on a spring in SHM has amplitude Aand period T. At what point in the motion is v = 0 and a = 0 simultaneously?

ConcepTest 13.2 Speed and Acceleration

1) x = A

2) x > 0 but x < A

3) x = 0

4) x < 0

5) none of the above

A mass on a spring in SHM has amplitude A and period T. At what point in the motion is v = 0 and a = 0 simultaneously?

If both v and a would be zero at the same time, the mass would be at rest and stay at rest! Thus, there is NO point at which both v and a are both zero at the same time.

Follow-up: Where is acceleration a maximum?

ConcepTest 13.6aPeriod of a Spring I

A glider with a spring attached to each end oscillates with a certain period. If the mass of the glider is doubled, what will happen to the period?

1) period will increase

2) period will not change

3) period will decrease

T = 2p (m/k)ConcepTest 13.6aPeriod of a Spring I

A glider with a spring attached to each end oscillates with a certain period. If the mass of the glider is doubled, what will happen to the period?

1) period will increase

2) period will not change

3) period will decrease

The period is proportional to the square root of the mass. So an increase in mass will lead to an increase in the period of motion.

Follow-up: What happens if the amplitude is doubled?

ConcepTest 13.8aPeriod of a Pendulum I

Two pendula have the same length, but different masses attached to the string. How do their periods compare?

1) period is greater for the greater mass

2) period is the same for both cases

3) period is greater for the smaller mass

T = 2p (L/g)ConcepTest 13.8aPeriod of a Pendulum I

Two pendula have the same length, but different masses attached to the string. How do their periods compare?

1) period is greater for the greater mass

2) period is the same for both cases

3) period is greater for the smaller mass

The period of a pendulum depends on the length and the acceleration due to gravity, but it does not depend on the mass of the bob.

Follow-up: What happens if the amplitude is doubled?

WAVES, VIBRATIONS, AND SOUND

TODAY’S AGENDA

Wednesday, January 24

- Simple Harmonic Motion
- Hw: Practice C (All) p381

UPCOMING…

- Wed: Measuring SHM
- Thur: Properties of Waves
- Problem Quiz #1
- Fri: Wave Interactions

Chapter 11

Vibrations and Waves

Units of Chapter 11

- Simple Harmonic Motion
- Energy in the Simple Harmonic Oscillator
- The Period and Sinusoidal Nature of SHM
- The Simple Pendulum
- Forced Vibrations; Resonance

The Simple Pendulum

So, as long as the cord can be considered massless and the amplitude is small, the period does not depend on the mass.

MIT Lec 10 Dr. Lewin (@ 20.30min. – 23.37min.)

MIT Lec 10 Dr. Lewin (@ 37.35 min. – End)

Forced Vibrations; Resonance

Forced vibrations occur when there is a periodic driving force. This force may or may not have the same period as the natural frequency of the system.

If the frequency is the same as the natural frequency, the amplitude becomes quite large. This is called resonance.

Mechanical Universe Caltech

Lec 17 (@ 25.13min. – 28.54 min.)

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