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let's get physical! > 13. and I'm on that new vibration [NTF] > Flashcards

13. and I'm on that new vibration [NTF] Flashcards

oscillations

1
Q

Simple Harmonic Motion

A

an oscillation where the acceleration of an object is directly proportional to is displacement from the equilibrium position.

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2
Q

conditions for simple harmonic motion

A
  • acceleration directly proportional to is displacement from the equilibrium position.
  • acceleration always towards equilibrium position
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3
Q

size of the force in simple harmonic motion

A

depends on the distance from the midpoint

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4
Q

time for one oscillation

A

is constant

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5
Q

as displacement from the midpoint increases…

A
  • acceleration increases

- velocity decreases

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6
Q

Energy in SMH

A

as the object moves towards the midpoint the restoring force does work on the object so it transfers some PE to KE. When the object is moving away from the midpoint it transfers it back again.

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7
Q

Max KE/ Zero PE position

A

midpoint/equilibrium position

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8
Q

Max PE/ zero KE position

A

maximum displacement

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9
Q

mechanical energy

A

a constant value which is the sum of all the KE and PE in the system

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10
Q

Displacement time graph

A

a cosine/sin curve with amplitude A.

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11
Q

Velocity time graph

A

the derivative of the displacement time graph. With max height Aω

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12
Q

Acceleration time graph

A

The derivation of the velocity time graph. With max height Aω^2

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13
Q

period, t

A

the time for one complete oscillation

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14
Q

frequency time period equation

A

f = 1/t

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15
Q

frequency

A

the number of complete oscillations per second

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16
Q

amplitude

A

the maximum displacement from the equilibrium position

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17
Q

acceleration equation

A

a = -ω^2x

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18
Q

angular frequency equation

A

ω = 2πf

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19
Q

displacement time graph is sin if…

A

the timing starts from the centre of oscillation

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20
Q

displacement time graph is cos if…

A

the timing starts from the maximum displacement

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21
Q

different types of simple harmonic oscillators…

A
  • pendulum
  • mass/spring
  • circular motion
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22
Q

When a mass on a spring is pulled/pushed either side of its equilibrium position there is a force exerted on it. This force is found by:

A

F = -kx

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23
Q

Coming F = -kx and F = ma gives

A

T = 2π√(m/k)

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24
Q

T = 2π√(m/k) condition

A
  • only for small oscillations

- for a mass and spring system

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25
Q

for a pendulum the time period can be found by…

A

T = 2π√(L/g)

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26
Q

T^2 α

for a simple pendulum

A

Length

27
Q

T doesn’t depend on…

for a simple pendulum

A

mass or amplitude

28
Q

amplitude α

for a simple pendulum

A

Energy put into the system

29
Q

Damping

A

air resistance slows the object down and energy is lost from the system by overcoming friction

30
Q

What happens during damping

A

time period remains the same while maximum displacement reduces due to it slowing down

31
Q

critical damping

A

damping that allows an object to move back to its equilibrium position as quickly as possible

32
Q

Overdamping

A

doesn’t oscillate and takes a long time to move back to its original position

33
Q

light damping

A

takes a long time for oscillations to die away

34
Q

heavy damping

A

oscillations die away quickly

35
Q

free oscillation

A

when you displace an object and then let it oscillate freely at its own natural

36
Q

forced oscillation

A

when you apply an external driving force to an oscillation

37
Q

natural frequency

A

the frequency of oscillations when there is no external force on the system

38
Q

resonance

A

when the frequency of the external driving force is the same/ close to the natural frequency causing energy transfer to be maximised and the amplitude to grow

39
Q

how is the effect of resonance reduced

A

damping absorbs energy therefore reduces the effect

40
Q

as damping increases…

A
  • amplitude of resonant peak decreases
  • resonance peak gets broader
  • resonant frequency gets lower (peak shifts to the left)
41
Q

uses of resonance

A
  • used in musical instruments
  • used to tune circuits for communication
  • used in digital watches
  • used in medicine: magnetic resonance imaging or ultrasounds
42
Q

dangers of resonance

A
  • violently shaking buses or washing
  • glass smashing
  • swaying bridges
43
Q

v (max) =

A

Aω

44
Q

PE =

A

1/2kx^2

45
Q

KE =

A

1/2mv^2

46
Q

rubber band causing damping

A

work is done on the rubber band so energy dissapates to the rubber band

47
Q

energy transfer in resonance

A

most efficient/ maximum transfer of energy

48
Q

conditions for resonance

A

frequency of the driving force must be the same/ similar to the natural frequency of the object

49
Q

a (max) =

A

Aω^2

50
Q

explain how sound is amplified

A

A sounding box vibrates. The box and the thing making the sound have the same/similar natural frequencies so resonance occurs. Energy is transfer to the sounding box resulting in a larger amplitude oscillation and louder sound.

51
Q

explain why amplified sound may die away faster.

A

The sounding box may dampen oscillations therefore a larger rate of energy transfer to the air.

52
Q

what remains constant during damping

A

time period

53
Q

when is the resultant force on a mass a minimum?

A

at the centre of oscillation

54
Q

explain how mass dampers work

A
  • The springs absorb energy because the springs oscillate with natural frequency of the object
  • Hence there is an efficient/maximum transfer of energy
  • Springs must not return energy to bridge so the energy is dissipated as quickly as possible
55
Q

What equations do you show to be true when verifying SHM ?

A 
a = ω^2x
T = 2π√(m/k)
56
Q

verifying SHM from a displacement time graph and an acceleration time graph

A
  • read of the heights and calculate the displacement from the equilibrium position for each one
  • plot acceleration against displacement
  • should be a straight line graph through the origin with negative gradient a = -ω^2x
57
Q

When will an object loose contact with an oscillating object

A

when the acceleration of oscillations is greater than g

58
Q

how to measure the frequency of oscillations

A

with a stop clock measure the time for ten oscillations. calculate the time period of one oscillation. use f = 1/t to calculate the frequency.

59
Q

what to include in long answer of experiment

A
  • apparatus
  • method
  • accuracy precautions
60
Q

derivative of cos

A

-sin

61
Q

derivative of sin

A

cos

62
Q

example of a forced oscillation

A

a car driving over a bridge

63
Q

The damping force acting on an oscillating system is always

A

in the opposite direction to the velocity.

64
Q

The restoring force on a spring system is always…

A

in the opposite direction to velocity

let's get physical! (20 decks)

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