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Physics and Math Correct Deck > Ch. 7: Waves and Sound > Flashcards

Ch. 7: Waves and Sound Flashcards

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1
Q

defn: sinusoidal waves

A

can be transverse or longitudinal

the individual particles oscillate back and forth with a displacement that follows a sinusoidal pattern

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2
Q

defn: transverse waves

A

those in which the direction of particle oscillation is perpendicular to the propagation (movement) of the wave

think about “the wave” in a stadium (they dont run around the stadium, they stand up or sit down)

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3
Q

what are three examples of electromagnetic transverse waves?

A
  1. visible light
  2. microwaves
  3. X-rays
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4
Q

in any waveform, what direction is energy delivered?

A

in the direction of wave travel

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5
Q

defn: longitudinal waves

A

waves in which the particles of the wave oscillate parallel to the direction of propagation

the wave particles are oscillating in the direction of energy transfer

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6
Q

what is a classic example of longitudinal waves?

A

sound waves

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7
Q

longitudinal waves oscillate through cycles of what?

A

compression and rarefaction (decompression)

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8
Q

defn: crest

A

one maximum of the wave

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9
Q

defn + symbol: wavelength

A

the distance from one maximum (crest) of the wave to the next

symbol: lambda

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10
Q

defn + unit: frequency

A

the number of wavelengths passing a fixed point per second

unit: hertz or cycles per second (cps)

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11
Q

defn: period (T)

A

the number of seconds per cycle

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12
Q

defn: equilibrium position

A

waves oscillates about this central point

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13
Q

defn: displacement (wave)

is it vector or scalar?

A

describes how far a particular point on the wave is from the equilibrium position

vector

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14
Q

defn: amplitude

A

the maximum magnitude of displacement in a wave

the maximum displacement from the equilibrium position to the top of a crest or bottom of a trough, not the total displacement between a crest and a trough (that is double the amplitude)

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15
Q

defn: phase difference

A

a wave of describing how “in step” or “out of step” the waves are when analyzing waves that are passing through the same space

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16
Q

defn: in phase

what is the phase difference?

A

consider 2 waves with the same frequency, wavelength, and amplitude and pass through the same space at the same time

we can say they are IN PHASE if their respective crests and troughs coincide (line up with each other)

the phase difference is 0

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17
Q

defn: out of phase

what is the phase difference?

A

if the two waves travel through the same space in such a way that the crests of one wave coincide with the troughs of the other then they are OUT OF PHASE

phase difference: one-half a wave

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18
Q

defn: the principle of superposition

A

when waves interact with each other, the displacement of the resultant wave at any point is the sum of the displacements of the two interacting waves

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19
Q

defn: constructive interference

A

when the waves are perfectly in phase, the displacements always add together and the amplitude of the resultant is equal to the sum of the amplitudes of the two waves

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20
Q

defn: destructive interference

A

when waves are perfectly out of phase, the displacements always counteract each other and the amplitude of the resultant wave is the difference between the amplitudes of the interact waves

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21
Q

defn: partially constructive interference

A

waves are not perfectly in phase with each other

mostly add together

displacement of the resultant: the sum of the displacements of the two waves (not quite the sum of the two waves amplitudes)

amplitude of the resultant: not quite the sum of the two waves’ amplitudes

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22
Q

defn: partially destructive interference

A

the two waves do not quite cancel, but the resultant wave’s amplitude is clearly much smaller than that of either of the other waves

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23
Q

defn: traveling wave

A

if a string fixed at one end is moved up and down, a wave will form and travel (propagate) toward the fixed end

it is called a traveling wave because it is moving

when the wave reaches the fixed boundary, it is reflected and inverted

if the free end of the string is continuously moved up and down, there will then be two waves: the original moving down the string toward the fixed end and the reflected wave moving away from the fixed end, these waves will then interfere with each other

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24
Q

defn: standing wave

A

both ends of the string are fixed and traveling waves are excited in the string

certain wave frequencies will cause interference between the traveling wave and its reflect wave such that they form a waveform that appears to be stationary

the only apparent movement of the string is fluctuation of amplitude at fixed points along the length of the string

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25
Q

defn: nodes

A

points in the wave that remain at rest (where amplitude is constantly zero)

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26
Q

defn: antinodes

A

points midway between the nodes fluctuate with maximum amplitude

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27
Q

what are the two scenarios in which standing waves can be supported?

A
  1. strings fixed at both ends
  2. pipes open at both ends
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28
Q

what is the third scenario that standing waves can be supported, but the mathematics are different? why is the math different?

A

pipes that are open at one end and closed at the other

why: closed end contains a node, open end contains an antinode

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29
Q

defn + aka: natural frequencies

A

aka: resonance frequenices

any solid object, when hit, struck, rubbed, or disturbed in any way will begin to vibrate

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30
Q

defn: timbre

A

the quality of sound, determined by the natural frequency or frequencies of the object

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31
Q

defn: noise

A

objects vibrate at multiple frequencies that have no relation to one another

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32
Q

defn: fundamental pitch + overtones

A

objects vibrate at multiple natural frequencies that are related to each other by whole number ratios producing a richer, more full tone

33
Q

what is the range of frequencies commonly audible by young adults?

A

20 - 20,000 Hz

34
Q

what are the three variables that the natural frequencies of a string depend on?

A
  1. length
  2. linear density
  3. tension
35
Q

defn: forced oscillation

A

if a periodically varying force is applied to a system, the system will then be driven at a frequency equal to the frequency of the force (force frequency)

36
Q

defn: resonating

A

if the frequency of the periodic force is equal to a natural (resonant) frequency of the system, then the system is resonating, and the amplitude of the oscillation is at a maximum

37
Q

defn + aka: damping

A

aka: attenuation

a decrease in amplitude of a wave caused by an applied or nonconservative force

38
Q

defn: sound

A

a longitudinal wave transmitted by the oscillation of particles in a deformable medium

39
Q

what can sound travel through (3) and not (1)?

A

yes:
1. solids
2. liquids
3. gases

not: vacuum

40
Q

defn: bulk modulus

A

a measure of the medium’s resistance to compression

41
Q

does B (bulk modulus) increase or decrease from gas to liquid to solid?

A

increase

42
Q

does sound travel fastest through a solid, liquid or gas?

does sound travel slowest through a solid, liquid, or gas?

why?

A

fastest: solid

slowest: gas

why? because the bulk modulus increases disproportionately more than density as one goes from gas to liquid to solid

43
Q

what is the speed of sound in air?

A

343 m/s

44
Q

how is sound produced?

A

by the mechanical disturbance of particles in a material along the sound wave’s direction of propagation

although the particles themselves do not travel along with the wave, they do vibrate or oscillate about an equilibrium position which causes small regions of compression to alternate with small regions of rarefaction

these alternating regions of increased and decreased particle density travel through the material, allowing the sound wave to propagate

45
Q

defn: frequency

A

the rate at which a particle or wave completes a cycle

46
Q

defn: pitch

A

our perception of the frequency of the sound

47
Q

defn: infrasonic waves

A

sound waves with frequencies below 20 Hz

48
Q

defn: ultrasonic waves

A

sound waves with frequencies above 20,000 Hz

49
Q

defn + laymen’s defn: Doppler effect

A

describes the difference between the actual frequency of a sound and its perceived frequency when the source of the sound and the sound’s detector are moving relative to one another

laymen: an ambulance of fire truck with its sirens blaring is quickly approaching from the other lane, and as it passes, one can hear a distinct drop in the pitch of the siren

50
Q

if the source and detector are moving toward each other, is the perceived frequency greater or less than the actual frequency? what is they are moving away from each other?

A

moving TOWARD: perceived > actual

moving AWAY: perceived < actual

51
Q

doppler equation sign convention mnemonic

A

Top sign for Toward

Bottom sign for away

52
Q

is the top or the bottom of the Doppler equation the source or the detector?

A

NUMERATOR = detector

DENOMINATOR = source

53
Q

defn + process: echolocation

A

the Doppler effect as used by animals

the animal emitting the sound serves as both the source and detector of the sound

the sound bounces off of a surface and is reflected back to the animal

how long it takes for the sound to return, and the change in the frequency of the sound, can be used to determine the position of objects in the environment and the speed at which they are moving

54
Q

defn: shock wave

A

highly condensed wave front

55
Q

how is a shock wave produced? (3)

A
  1. an object that is producing sound while traveling at or above the the speed of sound allows wave fronts to build upon one another at the front of the object
  2. this creates a much larger amplitude at that point
  3. because amplitude for sound waves is related to the degree of compression of the medium, this creates a large pressure differential or pressure gradient
56
Q

what is a possible effect of a shock wave?

A

can cause physical disturbances as it passes through other objects

57
Q

what causes a sonic boom?

A

the passing of a shock wave creates very high pressure, followed by very low pressure, which is responsible for a sonic boom

58
Q

when can a sonic boom be heard?

A

any time that an object traveling at or faster than the speed of sound passes a detector, not just at the point that the speed of sound is exceeded

59
Q

defn: Mach 1

A

the point at which the speed of sound is exceeded

60
Q

why are some of the effects of a shock wave mitigated?

A

because all of the wave fronts will trail behind the object, destructively interfering with each other

61
Q

defn: loudness/volume

A

the way in which we perceive a sounds intensity

62
Q

what is the main difference between a sounds intensity and a sounds loudness/volume?

A

intensity is objectively measurable

loudness/volume is subjective

63
Q

defn + SI units: intensity

A

the average rate of energy transfer per area across a surface that is perpendicular to the wave

the power transported per unit area

SI units: watts per square meter

64
Q

what is the impact of damping or attenuation on sound?

A

sound is not transmitted undiminished

even after the decrease in intensity associated with distance, real world measurements of sound will be lower than those expected from calculations

65
Q

why is sound subject to the same nonconservative forces as any other system?

A

because oscillations are a form of repeated linear motion

66
Q

what dictates the wavelengths of traveling waves that can establish standing waves?

A

the length of the medium

67
Q

defn + 2 examples: closed boundaries

A

those that do not allow oscillation and that correspond to nodes

ex:
1. closed end of a pipe
2. secured ends of a string

68
Q

defn + 2 examples: open boundaries

A

those that allow maximal oscillation and correspond to antinodes

  1. the open end of a pipe
  2. free end of a flag
69
Q

defn: harmonic

A

the number of half-wavelengths supported by the string

70
Q

defn + aka: fundamental frequency

A

the lowest frequency (longest wavelength) of a standing wave that can be supported in a given length of string

aka: first harmonic

71
Q

defn: harmonic series

A

all the possible frequencies that the string can support

72
Q

defn: open vs. closed pipes

A

open pipes = pipes that are open at both ends

closed pipes: closed at one end, open at the other

73
Q

what is another name for the second harmonic?

A

the first overtone

74
Q

how are harmonics of a closed pipe different?

A

the harmonic of a closed pipe is equal to the number of quarter wavelengths supported by the pipe NOT the number of half wavelengths like with strings or open pipes

75
Q

defn: ultrasound

A

uses high frequency sound waves outside the range of human hearing to compare the relative densities of tissues in the body

76
Q

how does an ultrasound machine create a graph and what does the graph respresent?

A

how: because the speed of the wave and travel time is known, cna calculate the traversed distance and ultimately relies on reflection

what: borders and edges within the body

77
Q

how does Doppler ultrasound work? for what?

A

used to determine the flow of blood within the body by detecting the frequency shift that is associated with movement toward or away from the receiver

78
Q

what are 4 ways ultrasound can be used therapeutically?

A
  1. promote healing by creating friction and heat when they act on tissues to increase blood flow
  2. focus sound wave using parabolic mirror to cause constructive interference to create a high-energy wave exactly at that point to break up a kidney stone or destroy small tumors
  3. dental cleaning
  4. cataract destruction

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