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Physics > Build or Bust > Flashcards

Build or Bust Flashcards

1
Q

What waves does an Earthquake have?

A

seismic waves

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2
Q

What seismic waves does an earthquake have?

A
  • P waves (primary)
  • S waves (secondary)
  • surface waves
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3
Q

Where is a P wave found?

A

its a body wave so is found all over the Earth - it is the first wave felt because it travels faster as mechanical waves are able to pass on energy more easily

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4
Q

Where is a S wave found?

A

its a body wave so if found all over the Earth but gets there second

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5
Q

Where are surface waves found?

A

only in the Earth’s crust

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6
Q

What type of waves are P and S waves?

A

P wave is a longitudinal wave

S wave is a transverse wave

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7
Q

Longitudinal wave

A

Oscillation of particles occur parallel to the direction of travel/ wave motion/ propagation/ energy transfer. Has compressions and rarefactions

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8
Q

Transverse wave

A

Oscillation of particles occur perpendicular to direction of travel/ propagation/ wave motion/ energy transfer

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9
Q

Young’s modulus equation

A

Stress / strain (measured in Nm^-2) could be Fl/Ax

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10
Q

What is Young’s modulus?

A

how much force is needed to make the 1x1x1 cube stretch by a certain amount

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11
Q

Find Young’s modulus of a material experiment

A

IV - force
DV - cross sectional area, original length, extension
Get a material measure the length of it and the cross sectional area. Use clamp, desk pulley, markers and metre ruler. Hang off edge of table, add force to hanging end and note how much a marker moves (this is the extension) Plot a graph of stress against strain, work out the gradient

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12
Q

What is the shadow zone?

A

the area waves aren’t felt

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13
Q

What material can’t transverse waves travel through very well?

A

transverse can’t travel through liquid very well (this includes S waves through the outer core)

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14
Q

Free oscillation

A

if an object is set vibrating it will oscillate at its natural frequency

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15
Q

Seismometer

A

earthquake is driver so we want the seismometer to have the same natural frequency

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16
Q

Amplitude

A

furthest distance from equilibrium (maximum point away from zero point)

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17
Q

How to measure the time period of a pendulum/ spring

A
  • displace pendulum (only a small displacement)
  • measure the time for 20 oscillations
  • full oscillation is time between passing the same point in the same direction (always measure from the mean position)
  • divide by 20 for time period of one oscillation
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18
Q

How can we reduce error when measuring period of pendulum?

A
  • to reduce parallax error use a Fiducial marker - 2 posts, put pendulum between them
  • increase overall oscillations measuring 20 instead of 10 or 30 instead of 20 this reduces uncertainty
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19
Q

How can you make a wine glass break?

A

Hit the wine glass once, it will oscillate at its natural frequency, if you match this frequency and hold it the glass will break. This is because maximum energy transfer is occurring so it won’t be able to withstand oscillations so will crack and then break

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20
Q

If the driver frequency equals the natural frequency…

A

…resonance will occur

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21
Q

What happens to the amplitude when resonance occurs?

A

the amplitude increases dramatically

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22
Q

Natural frequency

A

The frequency an object oscillates at when hit into motion. When driven at this frequency there will be violent movement. Also maximum amplitude occurs when maximum energy transfer happens because the natural frequency of the driver is the same as the driven

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23
Q

Resonance

A
  • when an object oscillates at its natural frequency

- if driven at this frequency amplitude will get bigger due to maximum energy transfer

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24
Q

Simple harmonic motion

A

Pull pendulum to one side, force pulling back to mean position. The further from mean position, bigger force pulling it back to equilibrium.
Force is proportional to displacement (from original position)
Displacement is proportional to acceleration

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25
Q

Object undergoing SHM

A
  • acceleration proportional to displacement from equilibrium position
  • acceleration in opposite direction to displacement
26
Q

Equations for SHM

A 
F = -kx
a = -kx
27
Q

Where is the force directed in SHM?

A

force is always directed towards the mean position

28
Q

In SHM the period is…

A

independent of the amplitude

29
Q

Energy when pendulum at equilibrium

A

Potential energy = 0

Kinetic energy = max

30
Q

Energy when pendulum at max amplitude

A

Potential energy = max

Kinetic energy = 0

31
Q

2 springs in parallel =

A

double stiffness

32
Q

The total amount of energy in the system of a simple harmonic oscillator is…

A

…constant - the kinetic and potential energy values change but the total energy doesn’t

33
Q

How can sound waves moving through a material be modelled?

A

as simple harmonic motion

34
Q

Stiffer material =

A

greater wave velocity through it

35
Q

Why does sound travel faster through hotter air?

A

because it has a lower density

36
Q

brittle

A

no plastic deformation before it cracks

37
Q

Fixed points

A

melting point of ice
boiling point of water
triple point of water

38
Q

Specific Heat capacity

A

the amount of energy required to raise 1kg by 1K (or degrees celsius)

39
Q

What happens to the oscillations when damping occurs?

A

oscillations reduce over time

40
Q

What causes damping?

A

normally due to friction or resistance

41
Q

Latent heat

A
  • energy required to change the state of 1kg (or g) of an object - change the intermolecular bonds (increase potential energy of particles or energy given out)
  • energy involved in a phase change
42
Q

Conduction

A

‘spreading’ through the material by atomic and molecular vibrations and motion of free electrons

43
Q

Convection

A

heating of a fluid, expands when heated, becomes less dense so rises, cooler denser fluid takes its place creating a convection current

44
Q

Radiation

A

energy lost by electromagnetic radiation, hotter object, shorter wavelength of emitted radiation

45
Q

What is needed to produce a phase change?

A

energy

46
Q

What is a phase change?

A

a change in state e.g. solid –> liquid or liquid –> gas

47
Q

Phase change materials

A

objects change state at certain temperatures

48
Q

Internal energy

A

sum of potential and kinetic energy in a group of particles

49
Q

What happens to the internal energy during a phase change?

A

during a phase change the internal energy will change

50
Q

TMD

A

tuned-mass damper

51
Q

What is an effective way to reduce resonance within a building?

A

to have a TMD

52
Q

What does a TMD do?

A

add massive pendulum or spring mass system that has the same natural frequency as the building
-If the building is driven to oscillate at same frequency, both structure and TMD will resonate. The TMD will oscillate in antiphase so amplitude of oscillations reduced

53
Q

Damping

A

-the amplitude of oscillations in a system that is not subject to an external driving force will decrease over time due to resistive forces within the system

54
Q

What is damping a consequence of in mechanical systems?

A

friction or viscous drag

55
Q

What do dampers do?

A

dissipate the energy

56
Q

Light damping

A
  • amount of energy lost within each oscillation is quite small
  • system oscillates several times before rest (swing door, oscillates several times before shutting)
57
Q

Critical damping

A

-something moves back to its equilibrium position as fast as possible but never quite beyond it

58
Q

Heavy damping

A

-the system takes a long time to return to equilibrium position then stays there without oscillating (door with stiff hinges, closes slowly)

59
Q

Heavier the damping…

A

…the quicker energy is lost from that system

60
Q

Damped system

A

absorb energy and vibrate when driven but resonate vibrations have smaller ‘spread’ over wide frequency range

61
Q

Damping can make an oscillating system come to rest more quickly, it can also…

A

…prevent it from resonating quite so violently when driven at its natural frequency

Physics (12 decks)

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