ch 7 - Waves and Sound Flashcards
sinusoidal waves
waves that may be transverse or longitudinal in which the individual particles oscillate back and forth with a displacement that follows a sinusoidal pattern.
transverse waves
those waves in which the direction of the particle oscillation is perpendicular to the propagation (movement) of the wave; ex are electromagnetic waves such as visible light, microwaves and x-rays
longitudinal waves
waves in which particles of wave oscillate parallel to the direction of propagation, oscillating in direction of energy transfer; ex sound waves
distance from one maximum (crest) of a wave to the next
wavelength represented by the upside down y
number of wavelengths passing a fixed point per second
frequency (f), measured in hertz (Hz) or cycles per second
propagation speed (v) of a wave
v = f x upside down y (propagation speed = frequency x wavelength
period equation (inverse of frequency)
T = 1/f. Period = 1/f, defines the number of seconds per cycle
angular frequency
fancy w = 2pi x f = (2pi)/T measured in radians per second
equilibrium position
central point around which waves oscillate
displacement (x)
in waves, describes how far a particular point on the wave is from the equilibrium position, vector quantity
amplitude (A)
maximum magnitude of displacement from the equilibrium position to the top of the crest or bottom of a trough, in a wave
phase difference
measure of how “in step” or “out of step” waves are. If in same place at same time with same amplitude, frequency and wavelength then phase difference = 0
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 displacements of the two interacting waves
constructive interference
in principle of superposition, when waves are perfectly in phase, the displacements are always the sum of the amplitudes of the two waves
destructive interference
in principle of superposition, when waves are perfectly out of phase, then the displacements are always the difference between the amplitudes of the two waves
travelling wave
moving wave from moving end of string or source to immobile end; if end is continuously moving waves will come back and still be going out and interfere with each other
standing waves
fluctuation of amplitude along fixed points along length of string or whatever waves are on;
nodes
points on something producing standing waves that remain at rest (where amplitude is constantly zero)
antinodes
points on something producing standing waves midway between the nodes that fluctuate with maximum amplitude
natural (resonant) frequencies
sounds that naturally come from certain objects
timbre
quality of sound; determined by the natural frequencies of an object
noise
scientifically it is produced by objects that vibrate at multiple frequencies that have no relation to one another
frequency range generally audible to health young adults
20 Hz to 20,000 Hz
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
resonating system
occurs when the frequency of the periodic force is equal to a natural (resonant) frequency of the system; amplitude of the oscillation is at a max
damping (attenuation)
a decrease in amplitude of wave caused by an applied or nonconservative force
equation for speed of sound
v = square root of (B/fancy p) where B is bulk modulus, a measure of medium’s resistance to compression (B increases from gas to liquid to solid), fancy p = density of the medium; fastest in a solid with low density and slowest in a gas with high density
approximate speed of sound in air
343 m/s
pitch
our perception of the frequency of sound
infrasonic waves
frequencies below 20 Hz
ultrasonic waves
frequencies above 20,000 Hz
Doppler effect equation
f’ = f ((v + or - v sub D)/(v - or + v sub S) if source and detector are moving toward each other perceived frequency (f’) is greater than actual. The inverse is also true. f is actual emitted frequency v is the speed of sound in the medium, v sub D = speed of the detector and v sub S = speed of the source; first sign should be used when detector or source is moving toward the other object (+ in numerator, - in denominator) and opposite for opposite
Mach 1
point at which the speed of sound is exceeded
shock wave
highly condensed wave form produced by object producing sound that is travelling at or above the speed of sound allows wave fronts to build upon one another at the front of the object creating a much larger amplitude at that point creating a large pressure differential or pressure gradient
sonic boom
passing of a shock wave which creates a very high pressure followed by a very low pressure.
loudness/volume of sound
the way in which we perceive sound’s intensity
intensity
objectively measurable; avg rate of energy transfer per area across a surface that is perpendicular to the wave; power transported per unit time: I (intensity)= P/A; P = power and A = area; assuming intensity is uniformly distributed
SI unit for intensity
watts per square meter (W/m^2)
softest sound intensity audible on avg
1 x 10^-12 W/m^2
intensity of sound at the threshold of pain for human hearing
10 W/m^2 with instant perforation of eardrum occurring at about 1 x 10^4 W/m^2
sound level (beta)
measured in decibels (dB), it is a logarithmic scale used to make range of sound intensities detected by humans easier to work with; equation is beta = 10 log I/I sub 0; I = intensity of sound wave, I sub 0 = threshold of hearing (1 x 10^-12 W/m^2)
change in intensity of sound, equation
Beta sub f = B sub i + 10 log (I sub f/I sub i) where I sub f/I sub i is the ratio of the final intensity to the initial intensity
nodes
points in standing waves with no fluctuation in displacement
antinodes
points in standing waves with maximum fluctuation
Closed boundaries
boundaries in standing waves that do not allow oscillation and that correspond to nodes
open boundaries
boundaries in standing waves that allow max oscillation and correspond to antinodes (open end of a pipe is an example of this)
equation that relates wavelength of standing wave and length of string that supports it
wavelength (upside down y) = 2L/n; n = positive nonzero integer called the harmonic which corresponds to the number of half-wavelengths supported by the string, L = length of string
Possible frequencies of string equation
f = (nv)/2L; v = wave speed, n = any nonzero positive integer
fundamental frequency
also called first harmonic; lowest frequency (longest wavelength) of a standing wave that can be supported in a given length of string
first overtone
also called second harmonic - given by n = 2 (frequency of standing wave); has one-half the wavelength and twice the frequency of the first harmonic
second overtone
also called third harmonic; frequency of the standing wave designated by n = 3
harmonic series
all possible frequencies that a string can support
open pipes
pipes that are open at both ends; equation for relationship between wavelength of standing wave and length of an open pipe that supports it, and possible frequencies equation are both the same as the string
closed pipes
pipes that are closed at one end and open at the other
equation that relates wavelength of a standing wave and the length of a closed pipe that supports it
wavelength (upside down y) = (4L)/n; where n can only be an odd integer (n = 1, 3, 5…)
frequency of standing wave in a closed pipe
f = (nv)/4L; where v = wave speed
ultrasound
uses high frequency sound waves outside range of human hearing to compare the relative densities of tissues 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
