waves and sound Flashcards
sinusoidal waves
may be transverse or longitudinal; individual particles oscillate back and forth
transverse waves
those in which the direction of particle oscillation is perpendicular to the propagation (movement) of the wave; or perpendicular to the direction of energy transfer
longitudinal waves
those in which the particles of the wave oscillate parallel to the direction of propagation; or wave particles are oscillating in the direction of energy transfer
wavelength (lambda)
the distance from one max crest of the wave to the next
frequency (f)
the number of wavelengths passing a fixed point per second; units are hertz (Hz) or cycles per sec (cps)
propagation speed (v)
v=f(lambda)
period (T)
number of cycles per secT=1/f
angular frequency (omega)
used in consideration of simple harmonic motion in springs and pendula
omega(w)=2(pi)f=2pi/T
displacement (x)
describes how far a particular point on the wave is from the equilibrium position expressed as a vector quantity
amplitude (A)
the max magnitude of displacement
in phase
when two waves have the same frequency, wavelength, and amplitude and pass through the same space at the same time; line up with each other
out of phase
when two waves travel through the same space in a way that the crests of one wave coincide with the troughs of the other
the principle of superposition
states that when waves interact with each other, the displacement of the resultant wave at any point is the sum of the displacement of the two interacting waves
constructive interference
occurs when waves are exactly in phase with each other; the amplitude of the resultant wave is equal to the sum of the amplitudes of the two interfering waves
destructive interference
occurs when waves are exactly out of phase with each other; the amplitude of the resultant wave is equal to the difference in amplitude between the two interfering waves
partially constructive/destructive
occur when two waves are not quite perfectly in or out of phase with each other; the displacement of the resultant is equal to the sum of the displacement of the two interfering waves
traveling waves
have continuously shifting points of maximum and minimum displacement
standing waves
are produced by the constructive and destructive interference of two waves of the same frequency traveling in opposite direction in the same space
antinodes
are points of maximum oscillation
nodes
are points where there is no oscillation
timbre
the quality of sound, determined by the natural frequency or frequencies of the object
what is the general audible frequency for adults?
between 20 and 20,000Hz; the higher frequencies decline with age
forced oscillation
when 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; forced frequency is increased the closer the forced oscillation is the natural frequency
resonating
when the frequency of the periodic force is equal to a natural (resonant) frequency of the system; the amplitude of the oscillation is at a max
damping (attenuation)
a decrease in amplitude of a wave caused by an applied or non-conservative force
sound
a longitudinal wave transmitted by the oscillation of particles in a deformable medium; can travel through solids, liquids, and gases, however not a vacuum
speed of sound
v= sqrt(B/p)
B=bulk modulus (measure of the mediums resistance to compression), increases from gas to liquid to solid p=density of the medium
speed of sound in air
343 m/s
how does sound travel?
particles do not travel along the wave, they vibrate or oscillate about an equilibrium position, which causes small regions of compression to alternate with small regions of decompression; sound propagates; its the alternating regions of increased and decreased particle density travel through the material
infrasonic waves
sound waves with frequencies below 20 Hz
ultrasonic waves
sound waves above 20,000 Hz
Doppler effect
a shift in perceived frequency of a sound compared to the actual frequency of the emitted sound when the source of the sound and its detector are moving relative to one another f'=f [(v(+/-)vd)/(v(-/+)vs)] f'=perceived frequency f=actual emitted frequency v=speed of sound in the medium vd=speed of the detector vs=speed of the source
what is the apparent frequency in comparison to the emitted frequency when the source and detector are moving toward each other?
the apparent frequency will be higher then the emitted frequency
what is the apparent frequency in comparison to the emitted frequency when the source and detector are moving away from each other?
the apparent frequency will be lower than the emitted frequency
what is the apparent frequency in comparison to the emitted frequency when the source and detector are moving in the same direction?
the apparent frequency will be higher, lower, or equal to the emitted frequency, depending on their relative speeds
when can a sonic boom occur?
when the source is moving at or above the speed of sound
intensity
loudness or volume of sound (sound level); the average rate of energy transfer per area across a surface that is perpendicular to the wave; power transferred per unit area; unit watts per meter squared (W/m^2)I=P/AP=powerA=area
sound level (beta)
units decibels (dBeta) Beta=10log (I/Io) I=intensity of the sound wave Io= the threshold of hearing (1 x 10^-12 W/m^2)
change in sound level
Bf=Bi + 10log(If/Ii)
attenuation
also called damping, loss of energy as sound waves travel over a distance decreasing the intensity; due to sound being subject to nonconservative forces like friction and viscous drag
when do standing waves occur?
whenever two waves of the same frequency traveling in opposite directions interfere with one another as they travel through the same medium
closed boundaries
are those that do not allow oscillation and that correspond to nodes
open boundaries
are those that allow maximal oscillation and correspond to antinodes
wavelength of a standing wave (strings and open pipes)
lambda= 2L/n
n=positive nonzero integer call the harmonic; corresponds to the number of half wavelengths supported by the strings (number of antinodes) L=length
frequency of standing wave (strings and open pipes)
f=nv/2L
v=wave speed
fundamental frequency
the lowest frequency (longest wavelength) of a standing wave that can be supported by a given length of string
wavelength of standing waves (closed pipes)
lambda= 4L/n
n=any odd integer (cant be even)
frequency of a standing wave (closed pipes)
frequency (f)= nv/4L
v=speed of the wave
ultrasound
uses high frequency sound waves outside the range of human hearing to compare the relative densities of tissues in the body; this kind of machine requires reflection to generate an image of the borders and edges in the body
Doppler ultrasound
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
