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Yr 13 Physics 13 - Oscillations > Resonance and Damping > Flashcards

Resonance and Damping Flashcards

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1
Q

what two types of oscillations are there

A

free and forced oscillations

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2
Q

when do free oscillations happen

A
  • when a system performs oscillations

- free from the influence of any forces from outside the system

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3
Q

what is a natural frequency

A
  • the frequency any oscillating system naturally chooses to oscillate at
  • when left alone to freely oscillate
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4
Q

how could you change the free oscillation of the pendulum into a forced oscillation

A
  • by externally exerting a force on the pendulum

- such as pushing the bob in the opposite direction its naturally oscillating to

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5
Q

what is the name of the frequency you have now forced the pendulum to oscillate at

A
  • the driving frequency

- specifically your driving frequency

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6
Q

what is resonance

A
  • a phenomenon which describes very large amplitude oscillations that occur
  • when a driving frequency matches the natural frequency of the system
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7
Q

why does the amplitude of an oscillation become very large during resonance

A
  • because the system is absorbing the extra energy from the driving frequency
  • this added to its natural frequency leads the increase of its amplitude
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8
Q

what is going on inside a washing machine that causes it to sometimes be loud or quiet

A
  • when loud the motor would be spinning at the same natural frequency of one of the panels
  • this resonance results in large amplitudes which therefore results in loud noises
  • when quiet the motors rotation generates vibrations at other frequencies that dont match the natural frequency of any part of the machine
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9
Q

what will a graph of vibrational amplitude against frequency show for the washing machine example

A
  • the line will be very shallow (at 0 basically) and have a very low gradient for most of the frequencies
  • then it will begin to steeply rise and peak quickly
  • only to quickly fall back down to low levels but be slightly higher than before
  • with some sort of turbulence following the line
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10
Q

what is the peak of that graph telling you

A
  • the frequency at which resonance occurs

- and therefore the natural frequency of the panel

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11
Q

there is a mass on a spring connected to a vibration generator connected to a signal generator. the mass on the spring is above a motion sensor that is connected to a computer that datalogs the height of the mass. what is the equation for the time period of the oscillation of the mass on a spring

A

T = 2pi * root of (m / k)

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12
Q

what do each of those variables mean

A
  • T= time period per oscillation
  • m = mass of mass on spring
  • k = spring constant
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13
Q

given that is the equation for time period, what is the equation for frequency and why

A
  • f = (1 / 2pi) * root of (k / m)

- because T = 1 / f

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14
Q

what is the specific name of this frequency

A

the resonant frequency

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15
Q

what does measuring the amplitude of forced oscillations allow us to find and why

A
  • the resonant (natural) frequency
  • because the forced oscillations are created from the driving frequency of the vibration generator
  • and this is in resonance with the natural frequency
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16
Q

how would we rearrange this equation to work out the mass

A
  • f^2 = (1 / 4pi^2) *( k / m)
  • f^2 = k / 4pi^2 m
  • m = k / 4pi^2 f^2
17
Q

therefore what is the equation for working out the spring constant

A

k = 4pi^2 f^2 m

18
Q

what are damped oscillations

A
  • oscillations which suffer a loss in energy each time they oscillate
  • reducing their amplitude each time
19
Q

if a system is performing simple harmonic motion at its natural frequency, what two things could practically cause the dissipation of energy in that system

A
  • a frictional force acting on the system

- or the plastic deformation of a ductile material in the system

20
Q

what is damping

A

the material or system causing an energy loss each damped oscillation

21
Q

what is an example of damping in a swinging pendulum

A

air resistance

22
Q

despite the amplitude of oscillations decreasing overtime, what still remains constant throughout

A

the time period for each oscillation

23
Q

what does it mean if a system is critically damped

A
  • damping occurs such that the oscillator returns to its equilibrium position in the quickest possible time
  • without going past that equilibrium position
24
Q

what would critical damping look like on a displacement-time graph

A
  • the line would start on the top of the displacement axis

- then gently plateau onto the time axis and rest on it

25
Q

what is overdamping

A
  • when the system has been damped too much

- causing the oscillator to take a very long time to return to its equilibrium position

26
Q

where is overdamping practically used

A

in car suspension systems

27
Q

what would overdamping look like on a displacement-time graph

A
  • the line would start at the top of the displacement axis
  • then gently begin to plateau similar to the critical damping line
  • but it would stake significantly longer for it to reach the time axis
  • on most graphs it doesnt even reach it, its just left there suspended in the air
28
Q

what would a normally damped (underdamped) line look like on a displacement-time graph

A
  • the line would start at the equilibrium position and begin to oscillate normally
  • but with each full oscillation the peaks become smaller
  • until the line is just hugging the time axis with minuscule amplitudes
29
Q

what would an undamped line look like on a displacement-time graph

A

like any other normal oscillation, having constant amplitudes

30
Q

what is the goal for most engineers when creating a damping system for an object

A

to create a good medium between underdamping, critical damping and severe overdamping

31
Q

what is a main issue engineers come across when trying to achieve this

A

one object can have multiple natural frequencies

32
Q

what kind of damping would we want a shock absorption system to have and why

A
  • critical damping
  • because we want to make sure the system returns to equilibrium without overshooting
  • thereby stopping the oscillations as quickly as possble
33
Q

how do opera singers break wine glasses with their voice

A
  • they sing at a pitch that matches the natural frequency of the wine glass
  • this causes resonance to occur within the wine glass
  • the very large amplitudes caused by resonance rattle the structure of the glass so much that it breaks
34
Q

what two properties do climbing ropes need to have and why

A
  • they need to be stretchy to avoid a sudden and painful stop to a fall
  • but they need to be stiff enough to bring the climber to a halt
35
Q

how is this balance created in a climbing rope

A
  • the rope consists of several woven strands

- there is a ratio of stretchy strands to stiff strands which make the ideal balance between a stretchy and stiff rope

Yr 13 Physics 13 - Oscillations (4 decks)

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