SHM - Forced vibrations & resonance *was missed* Flashcards Preview

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Flashcards in SHM - Forced vibrations & resonance *was missed* Deck (10):
1

What is a periodic force?

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

 

 

2

What is a systems natural frequency?

  • when a system oscillates without a periodic force

 

 

3

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

  • 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?

  • 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?

  • 1/2π

 

6

What is resonance?

  • 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?

  • the freq at the maximum amplite is the resonant frequency 

 

 

8

What affect does damping have on resonance?

  • 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

9

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

  • 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?

  • 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