Ch. 7: Waves and Sound Flashcards
defn: sinusoidal waves
can be transverse or longitudinal
the individual particles oscillate back and forth with a displacement that follows a sinusoidal pattern
defn: transverse waves
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)
what are three examples of electromagnetic transverse waves?
- visible light
- microwaves
- X-rays
in any waveform, what direction is energy delivered?
in the direction of wave travel
defn: longitudinal waves
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
what is a classic example of longitudinal waves?
sound waves
longitudinal waves oscillate through cycles of what?
compression and rarefaction (decompression)
defn: crest
one maximum of the wave
defn + symbol: wavelength
the distance from one maximum (crest) of the wave to the next
symbol: lambda
defn + unit: frequency
the number of wavelengths passing a fixed point per second
unit: hertz or cycles per second (cps)
defn: period (T)
the number of seconds per cycle
defn: equilibrium position
waves oscillates about this central point
defn: displacement (wave)
is it vector or scalar?
describes how far a particular point on the wave is from the equilibrium position
vector
defn: amplitude
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)
defn: phase difference
a wave of describing how “in step” or “out of step” the waves are when analyzing waves that are passing through the same space
defn: in phase
what is the phase difference?
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
defn: out of phase
what is the phase difference?
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
defn: the principle of superposition
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
defn: constructive interference
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
defn: destructive interference
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
defn: partially constructive interference
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
defn: partially destructive interference
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
defn: traveling wave
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
defn: standing wave
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
defn: nodes
points in the wave that remain at rest (where amplitude is constantly zero)
defn: antinodes
points midway between the nodes fluctuate with maximum amplitude
what are the two scenarios in which standing waves can be supported?
- strings fixed at both ends
- pipes open at both ends
what is the third scenario that standing waves can be supported, but the mathematics are different? why is the math different?
pipes that are open at one end and closed at the other
why: closed end contains a node, open end contains an antinode
defn + aka: natural frequencies
aka: resonance frequenices
any solid object, when hit, struck, rubbed, or disturbed in any way will begin to vibrate
defn: timbre
the quality of sound, determined by the natural frequency or frequencies of the object
defn: noise
objects vibrate at multiple frequencies that have no relation to one another
defn: fundamental pitch + overtones
objects vibrate at multiple natural frequencies that are related to each other by whole number ratios producing a richer, more full tone
what is the range of frequencies commonly audible by young adults?
20 - 20,000 Hz
what are the three variables that the natural frequencies of a string depend on?
- length
- linear density
- tension
defn: forced oscillation
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)
defn: resonating
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
defn + aka: damping
aka: attenuation
a decrease in amplitude of a wave caused by an applied or nonconservative force
defn: sound
a longitudinal wave transmitted by the oscillation of particles in a deformable medium
what can sound travel through (3) and not (1)?
yes:
1. solids
2. liquids
3. gases
not: vacuum
defn: bulk modulus
a measure of the medium’s resistance to compression
does B (bulk modulus) increase or decrease from gas to liquid to solid?
increase
does sound travel fastest through a solid, liquid or gas?
does sound travel slowest through a solid, liquid, or gas?
why?
fastest: solid
slowest: gas
why? because the bulk modulus increases disproportionately more than density as one goes from gas to liquid to solid
what is the speed of sound in air?
343 m/s
how is sound produced?
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
defn: frequency
the rate at which a particle or wave completes a cycle
defn: pitch
our perception of the frequency of the sound
defn: infrasonic waves
sound waves with frequencies below 20 Hz
defn: ultrasonic waves
sound waves with frequencies above 20,000 Hz
defn + laymen’s defn: Doppler effect
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
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?
moving TOWARD: perceived > actual
moving AWAY: perceived < actual
doppler equation sign convention mnemonic
Top sign for Toward
Bottom sign for away
is the top or the bottom of the Doppler equation the source or the detector?
NUMERATOR = detector
DENOMINATOR = source
defn + process: echolocation
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
defn: shock wave
highly condensed wave front
how is a shock wave produced? (3)
- 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
- this creates a much larger amplitude at that point
- because amplitude for sound waves is related to the degree of compression of the medium, this creates a large pressure differential or pressure gradient
what is a possible effect of a shock wave?
can cause physical disturbances as it passes through other objects
what causes a sonic boom?
the passing of a shock wave creates very high pressure, followed by very low pressure, which is responsible for a sonic boom
when can a sonic boom be heard?
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
defn: Mach 1
the point at which the speed of sound is exceeded
why are some of the effects of a shock wave mitigated?
because all of the wave fronts will trail behind the object, destructively interfering with each other
defn: loudness/volume
the way in which we perceive a sounds intensity
what is the main difference between a sounds intensity and a sounds loudness/volume?
intensity is objectively measurable
loudness/volume is subjective
defn + SI units: intensity
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
what is the impact of damping or attenuation on sound?
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
why is sound subject to the same nonconservative forces as any other system?
because oscillations are a form of repeated linear motion
what dictates the wavelengths of traveling waves that can establish standing waves?
the length of the medium
defn + 2 examples: closed boundaries
those that do not allow oscillation and that correspond to nodes
ex:
1. closed end of a pipe
2. secured ends of a string
defn + 2 examples: open boundaries
those that allow maximal oscillation and correspond to antinodes
- the open end of a pipe
- free end of a flag
defn: harmonic
the number of half-wavelengths supported by the string
defn + aka: fundamental frequency
the lowest frequency (longest wavelength) of a standing wave that can be supported in a given length of string
aka: first harmonic
defn: harmonic series
all the possible frequencies that the string can support
defn: open vs. closed pipes
open pipes = pipes that are open at both ends
closed pipes: closed at one end, open at the other
what is another name for the second harmonic?
the first overtone
how are harmonics of a closed pipe different?
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
defn: ultrasound
uses high frequency sound waves outside the range of human hearing to compare the relative densities of tissues in the body
how does an ultrasound machine create a graph and what does the graph respresent?
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
how does Doppler ultrasound work? for what?
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
what are 4 ways ultrasound can be used therapeutically?
- promote healing by creating friction and heat when they act on tissues to increase blood flow
- 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
- dental cleaning
- cataract destruction
