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Physics > Exam 3 --141 > Flashcards

Exam 3 --141 Flashcards

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1
Q

Pressure

A

force spread out over an area

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2
Q

What is the unit of pressure?

A

a Pascal (Pa)

N/m2

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3
Q

What happens to pressure you exert on ground if you stand on one foot?

A

pressure increases since area decrease

area has an inverse relationship with pressure

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4
Q

What does pressure directly depend on in tank of water?

A

depth

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5
Q

Why do we not feel atmospheric pressure even though it is so large?

A

our bodies are not air tight

air inside our bodies pushes out just as hard as the atmosphere pushes in

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6
Q

Magdeberg sphere example

A

when a sphere has air inside of it you can easily split the sphere in half

when the air is removed from the sphere, you have to overcome atmospheric pressure to open and it becomes hard

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7
Q

Does pressure have direction?

A

no

pressure is a scalar

pressure can give a force perpendicular to any surface

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8
Q

What is true of static fluids?

A

pressures at the same horizontal level are equal

since not moving, all pressure cancels out and are the same on a horizontal level

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9
Q

Pascal’s principle

A

an increase in pressure is transmitted uniformly all through a fluid

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10
Q

How do you use a barometer to measure atmospheric pressure?

A

pressure measured in the barometer equals the atmospheric pressure

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11
Q

Buoyant force

A

contact force when fluids come into contact with an object

buoyant force always points upwards

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12
Q

Archimede’s principle

A

an object feels an upward bouyant force equal to thee weight of the fluid that is displaced

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13
Q

How to quantify the amount submerged of an object?

A

volume of displaced fluid equals the volume of the object submerged

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14
Q

What is true of force when an object is stably floating?

A

force in the y equals 0

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15
Q

What are two ways to quantify how fast a fluid flows?

A

1) focus on one molecule and see how many m/s the molecule covers
2) look at a cross-sectional gate and see what volume of a fluid passed through the cross-section over time (known as the flow rate)

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16
Q

Flow rate

A

volume / time that crosses through a cross-section

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17
Q

Why does syrup start thicker and thins as it falls?

A

flow rate remains constant and flow rate = Av

since v increases as you fall, A has to decrease to make up for increase in v and remain constant

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18
Q

Bernoulli’s equation

A

energy conservation for fluids

allows us to predict velocities of fluids

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19
Q

Where can energy hide in fluids?

A

pressurization, motion and gravity

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20
Q

Do faster moving fluids exist at higher or lower pressures?

A

faster moving fluids exist at lower pressures

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21
Q

Simple harmonic oscillators

A

a subgroup of oscillators that follow the mathematical form:

accleration = -w^2x

mirrors the fact that we have a linear restoring force

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22
Q

What is w^2 in oscillation?

A

k/m

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23
Q

Amplitude

A

distance from equilibrium to max/min (A)

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24
Q

Period

A

time for one complete back and forth motion (T)

goes through all points

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25
Q

Frequency

A

how many oscillations occur per time (f)

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26
Q

How are frequency and period related?

A

they are reciprocals

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27
Q

Spring force

A

a restoring force that acts towards equilibrium

force is linear (gets larger further away from equilibrium)

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28
Q

What type of forces are all simple harmonic oscillators governed by?

A

linear restoring force

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29
Q

What is acceleration at equilibrium of a simple harmonic oscillator?

A

a=0

since F=ma and F=-kx and x=0

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30
Q

What do you get when you compile many individual oscillations?

A

a wave

no single oscillator makes progress but the wave/disturbance does travel

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31
Q

2 broad classes of waves

A

transverse waves

longitudinal waves

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32
Q

Transverse waves

A

when any one oscillator moves it’s motion is perpendicular to the wave’s travel direction

ex: stadium wave

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33
Q

Longitudal waves

A

when any one oscillator moves it’s motion is parallel to the wave’s travel direction

ex: slinky

34
Q

What is the compression of a longitudal wave represented by graphically?

A

it is like the max/crest of the transverse wave

35
Q

What is the rarefaction (expanding) of a longitudal wave represented by graphically?

A

it is like the min/trough of the transverse wave

36
Q

What happens if you shake your hand faster and faster for a string wave?

A

the velocity is medium dependent so it does not change

the frequency is source dependent so it will increase

have to decrease wavelength as frequency increases to make velocity remain constant

v=wavelength * frequency

37
Q

Constructive interference

A

add together amplitudes to get bigger wave

38
Q

Destructive interference

A

subtract amplitudes to get smaller wave

39
Q

What type of waves are sound waves?

A

longitudal vibration

40
Q

Rank the velocity of sound in different mediums

A

solid > liquid > air

in a solid molecules are close together so easy to transfer the vibration of the wave

41
Q

How loud is sound?

A

picture-wise: loudness corresponds to the amplitude of the wave

quantitatively: loudness depends on source’s strength and the observer’s distance from the source

42
Q

Source’s strength

A

how much energy per time the source puts out

measured in J/s which is known as a Watt

power

43
Q

Why does loudness decrease further from the source?

A

you hear less units of sound since the units of sound spread out in an increasing radius

44
Q

Intensity

A

a linear scale that measures power/area

W/m2

45
Q

How do we rescale intensity of sound?

A

use a log scale of either 10^Bell or 10^Beta/10

Beta is the number of decibels

46
Q

Doppler effect

A

when an observer recieves a different frequency (pitch) than the source is emitting because of motion of the source and/or observer

ie. moving changing the pitches of sound you hear

47
Q

What happens if the source is moving forward, towards the observer?

A

this shortens the wavelength the observer hears

48
Q

What happens if the observer is moving towards the source?

A

makes the observer recieve more waves per second than the should and increases frequency

49
Q

What happens if the source is going faster than the speed of sound?

A

energy gets compressed and you get sonic boom from all the sound waves hitting at once in shock cone

50
Q

beats

A

what you get when two waves of almost the same pitch but not quite overlap and interfere with each other

amplitude (loudness) fades in and out

bigger difference in frequency will lead to more fading in/out per second

51
Q

standing waves

A

the phenomenon that essentially all instruments rely upon to produce one freq/note on demand without getting random frequencies

the wave does not travel

the amount of nodes matters

52
Q

How do you move up in a harmonic?

A

you add a node to a standing wave

53
Q

In a pipe where are the nodes?

A

each open-end of the pipe has an anti-node

54
Q

What are higher harmonics good for?

A

higher harmonics give tone

when you pluck a string, all the harmonics are simultaneously excited but you only hear the fundamental frequency

the higher harmonics are what makes a harp sound different from a guitar

55
Q

Heat

A

that which flows between objects of different temps

flows from hot to cold

56
Q

What do we measure heat in?

A

calories

57
Q

Temperature

A

measure of how quickly the objects in a molecule vibrate

58
Q

What is the prerequisite for a heat transfer?

A

a temperature difference

59
Q

why does metal feel colder then plastic even though they are at the same temperature?

A

metals are good heat conducters so heat leaves your hand to transfer to the metal quicker than heat leaves your hand for the plastic

60
Q

What is the symbol for heat transfer?

A

Q

+ means that heat flows into the object
- means that heat flows out of the object

61
Q

what does converting calories to joules show us?

A

that both heat transfers and work are transfers of Energy

leads to the 1st law of thermodynamics

62
Q

what is mechanical work in a piston?

A

pressure * the change in volume

  • when using the formula have volume units in m3
  • have pressure units in N/m^2
63
Q

What are two characteristics of an engine?

A

must operate on a reset-able cycle

must perform useful work on environment

64
Q

What does a single point on a Pv diagram correspond to?

A

one specific state of the piston

can only have a specific temperature when P and v are determined from graph

65
Q

List the steps of car engine

A

1) light a fire under gas and let the piston expand
2) lock piston in place and connect to a cold reservoir (energy flows out)
3) compress the piston while exposing to a cold reservior for a long time
4) lock the piston and light a fire under it (return to original state)

66
Q

What should ∆U of the entire system of an engine be?

A

should be zero

you should end up at same temperature that you started at

67
Q

What do we approximate ∆U to be?

A

∆T

68
Q

Why can an engine not be 100% efficient?

A

friction and you need a non-zero Qcold due to the second law of thermodynamics

69
Q

Second law of thermodynamics

A

in any physical process, the overall entropy of the universe must increase

70
Q

Second law of thermodynamics and Qcold

A

When you decrease from hot to cold, you are losing entropy (Qhot)

therefore, you need a Qcold to go from cold to hot and increase entopy

71
Q

Difference between positive and negative sign in work formula for piston?

A

positive sign in formula refers to work done by the gas

negative sign in formula refers to work done on the gas

72
Q

How to calculate work if pressure is not constant?

A

have to take the “integral” ie. the area under the curve

73
Q

What is the sign of the work done on the gas if the gas is expanding?

A

negative

74
Q

What is the sign of the work done by the gas if the gas is expanding?

A

positive

*increase in energy

75
Q

what is the sign of the work done on the gas if the gas is compressing?

A

positive

76
Q

What are the units when calculating the Carnot efficiency>

A

need to have temperatures in kelvin

77
Q

What direction do liquids flow in?

A

liquid flow from areas of high to low pressure

78
Q

How does Archimedes’ principle work as a thought experiment?

A

replace the volume of the object with the correpsonding volume of water

the surrounding frame of water can hold up that volume of water

if you place an object, the same force that was holding the water must hold the object

and the force holding up the water was equal to the weight of the water so the force holding up the object also equals the weight of the water

79
Q

Why does a floating object not sink due to atmospheric pressure?

A

the increase in atmospheric pressure is distributed equally through all depths, so there is no overall change

Pascal’s principle

80
Q

What do you use to find the velocity of springs?

A

use energy

81
Q

In transverse wave, do individual oscillators move left/right?

A

NO

They only move up/down. There is no movement for individual oscillators in the left/right direction

Physics (7 decks)

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