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14_Sound

Terms in this set (53)

What will always be the source of a sound wave?
Sound waves originate from a vibrating object and will moves outwards in all directions;
compression
the crest of a [longitudinal] sound wave; regions of sound waves were molecules are close together; regions of high pressure in the sound wave;
rarefaction
trough of a sound wave; region on wave where molecules are far apart ; regions of lower pressure in the sound wave;
Describe a sound wave
A sound wave is analogous to a slinky. When segments of the slinky coils are close together this corresponds to a compression[or the crest] when segments of the coils are spread far apart this corresponds to rarefactions[troughs]. The width of the slinky corresponds to the amplitude.
Why are sound waves considered to be longitudinal waves?
Because the vibrations of air molecules are parallel to the direction the sound wave travels.

because the displacement of the wave is parallel to the path[or direction] the wave travels
audible waves
sound waves with frequencies between 20 to 20,000 Hz that can be heard by humans.
infrasonic sound waves
sound waves with frequencies below audible sound[20 Hz] and can't be heard by humans. An earthquake wave is an example of infrasonic sound;
ultrasonic sound waves
sound waves above the audible level[20,000 Hz]; Examples include whistles and medical imaging instruments. Ultrasonic sound waves have high energies and short wavelengths
Threshold of Hearing
the smallest value of sound intensity [faintest sound] that the human ear can detect at a frequency of 1000 Hz. The numerical value is 1.0E-12 W/m2. this value is a constant and is used in the decibel equation. It is represented by variable Io.
Decibel level
A measure of loudness; Decibel level is referenced to the threshold of hearing and is calculated via logarithm;
pitch
the "human perception" of frequency.

an unscientific measure of how high or low a sound frequency is;

sound is described as having high pitch if the frequency is large and low if the frequency is small.
What does the speed of sound depend on?
The speed of sound depends on two things. [1] the state of mater for the medium. Because sound waves are vibrations the speed of it depends on how quickly one particle can transfer its motion to another. In a solid the molecules are so close together that, the disturbance happens quicker than in a gases. [2] for sound traveling in a gas, the speed of sound also depends on temperature. At higher temperatures, the molecules of a gas collide more. So the disturbance caused by the sound spreads faster at high temperatures than at low temp. In liquids and solids, particles are reasonable close enough together that the difference due to temperature is fairly negligible. IT should be noted that there are equations to calculate how each factor changes speed of sound but these equations are not included
Spherical wave
wave that radiates in all directions when a spherical object oscillates.
wave fronts
a series of circular arcs that represent a portion of a spherical wave emanating from a spherical vibrating object[looks like the WIFI symbol on many computers]. The distance between adjacent wave fronts equals the wavelength of the wave.
rays
a line [drawn perpendicular to wave fronts] that show the direction the wave moves.
plane waves
waves with parallel[ not concentric] wave fronts. plane waves exist when the spherical waves are far from their source of origin. They can be thought of as one-dimensional waves.
Doppler Effect
the perceived change in frequency [or loudness] of sound[light, or any wave] when there is relative motion between a source of sound and a listener. In the example of a moving ambulance the siren's frequency [loudness] doesn't change and should have the same loudness regardless of its position. However, the listener perceives the siren as louder[higher frequency] when the ambulance moves towards him/her and as quieter as it moves away.
Doppler Effect Case 1: "The Observer is Moving Relative to a Stationary Source"
An observer moving toward a stationary point source should hear a frequency that is GREATER than the source frequency. If the observer is moving away from the sound source the listener should hear a frequency SMALLER than the source frequency.
Doppler Effect Case 2: "The Source is moving Relative to a stationary observer"
The observed frequency increases as the source is moving toward the observer and the frequency decreases as the source moves away from the observer.
Doppler Equation 1( + ,- ) sign conventions for velocity of observer & velocity of source
When moving away velocity of observer & source have negative values. When moving towards, velocities has positive values.
Doppler Equation 1( + ,- )
Doppler Equation 2( - ,- ) sign conventions for velocity of observer & velocity of source
The positive direction is defined as from the source towards the detector.
Doppler Equation 2( - ,- )
Doppler Equation 3( + ,+ ): sign conventions for velocity of observer & velocity of source
v(r), is positive if the receiver is moving towards the source (and negative in the other direction); v(s), is positive if the source is moving away from the receiver (and negative in the other direction). [copy prompt & insert image]
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Doppler Equation 3( + ,+ ):
Why is ultrasound imaging done with high frequency sound waves [ultrasonic waves] than low frequency waves[infrasonic waves]?
ultrasonic sound waves have smaller wavelengths and reflect better off small objects than low frequency sound waves. Low frequency waves tend to wrap around objects and don't reflect back well.
sound Intensity
the rate at which (sound) energy moves through a unit of area. Just as frequency of a sound wave determines pitch, sound intensity determines perceived loudness.
Equation for sound Intensity
forced vibrations
when the vibration of one object causes other object to vibrate as well.
standing waves
a wave that moves back and forth between two fixed points[boundaries] appearing to stand still.

waves that appear to standstill
natural frequency
the frequency at which a system tends to oscillate in the absence of any driving or dampening force.
Node
[1]in a standing wave, it is the location where vibration does not occur; [2] point where two traveling waves always have the same magnitude of displacement but opposite signs, so that the net displacement is zero at that point in a standing wave.
Antinodes
area where vibrations occur in a standing wave; a location of maximum displacement;
What is the relationship between wavelength and nodes for standing waves?
The distance between any two consecutive nodes is always half the wavelength. Or the distance between a node and an antinode is 1/4 of the wavelength.
What is the relationship between frequency and antinodes for standing waves?
The number of antinodes[or loops in the string] equals the integer value of the frequency or harmonic number.
fundamental frequency
the lowest frequency of vibration for a vibrating string; This frequency corresponds to a standing wave with 1 antinode[or 1 loop in the string] & 2 nodes; Its also the frequency when the wavelength equals 1/2 the Length of the string[ or 2 times wavelength equals L]; fundamental frequency is also called the first harmonic;
First harmonic
the lowest frequency of a standing wave; it is frequency with only one antinode, one loop and frequency integer 1; it is the frequency when 1/2 wavelength equals L or wavelength equals 2L; frequency where standing wave has two nodes;
Second harmonic
second lowest frequency of a standing wave; this harmonic contains two antinodes, two loops in string and a frequency integer of 2; it has 3 antinodes. This frequency corresponds to wavelength equal to string length, L. second harmonic is also referred to as the first overtone;
First Overtone
another name for the second harmonic; this overtone has the second lowest frequency of a standing wave, contains two antinodes, two loops and frequency integer 2; it has 3 antinodes. This frequency corresponds to wavelength equal to string length, L.
Third harmonic
third lowest frequency of a standing wave that has 3 antinodes, has frequency integer 3, contain 3 loops, and has it 3/2 wavelength equals L or the wavelength equals 2/3 L. third harmonic is also known as 2nd overtone.
2nd Overtone
overtone that corresponds to the third lowest frequency of a standing wave. It is the overtone that has 3 antinodes, has frequency integer 3, contain 3 loops, and 3/2 its wavelength equals L or the wavelength equals 2/3 L. third harmonic is also known as 2nd overture.
Harmonics
a series of standing waves that have whole number integer frequencies;
How can the frequencies of string musical instruments be varied?
Frequencies of an instrument can be changed by varying either tension or length of the string.
What is resonance?
Resonance is a unique phenomenon where an external force, a vibrating object, or sound waves cause another object to vibrate or oscillate at its natural frequency; When this happens glasses can shatter [or emit sound] objects can vibrate, and bridges can break.
How can standing waves be created in an air column?
Standing longitudinal waves can be set up in a tube of air, such as an organ pipe, as the result of interference between sound waves traveling in opposite directions [specifically the incident & reflected waves]. If one end of the tube is closed, a node must exist at that end because the movement of air is restricted. If the ends are open, the elements of air have complete freedom of motion, and both ends are antinodes.
Equation for frequency of a Harmonic series
Equation for frequency of Harmonic series for a pipe open at both ends
Equation for frequency of a Harmonic series for a pipe open at one end
Harmonic series for a pipe open at both ends
this series is the same as a string.
Harmonic series for a tube with a closed end
there are no even multiples of the fundamental harmonic series. If a pipe is open at one end and closed at the other the fundamental frequency only has a node and an antinode. Therefore the length of the tube equals 1/4 wavelength.
What does it mean to be out of phase?
A scenario where the frequency of two waves are not equivalent...at different points in time the waves will alternate between interfering constructively and destructively.
Beats
a rhythmic interference of close frequencies out of phase. It sounds like a wowon-wowon sound. An alternation of loudness caused by two close but out of phase frequencies caused by the sound waves transitioning between constructive and destructive interference.
sound intensity
a measure of the loudness of a sound; it is the rate at which sound energy moves through a certain area;
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