Flashcards in SHM - Forced vibrations & resonance *was missed* Deck (10):

1

What is a periodic force?

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- force applied at regular intervals
- e.g. pushing swing

2

What is a systems natural frequency?

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- when a system oscillates without a periodic force

3

What are forced vibrations? What does the response of the system depend on?

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- when a periodic force is applied, the response depends on the fequency of the periodic force
- the system undergoes forced vibrations, when a periodic force is applied to it

4

What happens as applied frequency increases?

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- amplitude of oscillations increases until it reaches a maxiumum amplitude at a paticular freq, then decreases again
- the phase difference between the displacement and the periodic force increases from zero to 1/2π at the max amplitude, then from 1/2π to π as the freq increases further

5

What is the phase difference between the displacement and the periodic force at max amplitude?

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- 1/2π

6

What is resonance?

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- when the periodic force is exactly in phase with the velocity of the oscillating system (1/2 π phase difference)
- forced vibration frequency = natural frequency of systyem
- maximum transfer of energy
- no damping
- max amplitude

7

What is the resonant frequency?

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- the freq at the maximum amplite is the resonant frequency

8

What affect does damping have on resonance?

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- the lighter the damping,
- the larger the maximum amplitude becomes at resonance
- the closer the resonant freq is to the natural freq of the system

- no damping at resonance:
**the applied freq of the periodic force = the natural freq of the system**

- the larger the maximum amplitude becomes at resonance
- the closer the resonant freq is to the natural freq of the system

**the applied freq of the periodic force = the natural freq of the system**

9

What happens as the applied frequency becomes larger than the resonant frequency of the mass-spring system?

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- amplitude decrease more and more
- phase difference between the displace and the periodic force increases from 1/2π until the displace is π radiants out phase with the periodic force

10

What causes damping in a simple pendulum? What is the affect of adding mass?

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- damping caused by air resistance
- given same area
- bob with more mass has more kinetic energy at the same amplitude
- smaller fraction of energy removed per oscillation
- #intertia of heavier bob greater

- bob with more mass has more kinetic energy at the same amplitude
- smaller fraction of energy removed per oscillation
- #intertia of heavier bob greater