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Chapter 26 Physics

what is sound? sound is a form of energy that spreads out through space
what do vocal chords do to make noise? a singers vocal chords vibrate and cause neighboring air molecules to be set in motion, ripples in the form of a longitudinal wave travel through the air, frequency of the ripples match the frequency of the singers vibrating vocal chords, ripples hit the
eardrum and the eardrum is pushed and pulled with the same frequency, vibrations send rhythmic electrical impulses to the brain which result in the sound of the voice
where do sounds originate? in the vibrations of material objects, all sound is produced by vibrations of an object, string-piano,violin,guitar reed-saxophone, column of air-flute, vocal chords-voice
how big is the original vibration? original vibration may be small but it causes something larger to start vibrating, sounding board-stringed instrument, air column-reed/wind instrument, air in throat/mouth-person
what do these vibrations do? they create disturbance in surrounding medium (air) in the form of longitudinal waves, frequency of the vibrating object equals the frequency of the wave produced
how do we describe frequency? we describe how we hear frequency as pitch
how are frequencies and pitches related? high pitch equals high frequency, different musical notes have different pitches
what are the human sound limits? 20-20,000 Hz
how do human hearings change? as humans age they lose hearing in the higher frequencies first, below 20 Hz is INFRA*sonic (below) above 20,000 Hz is ULTRA*sonic (above
what are animals hearing limits? dogs can hear above 40,000 Hz, bats can hear above 100,000 Hz
what happens when a source of sound vibrates? a series of compressions and rarefactions travels outward from the source
what does opening and closing a door do? it produces compressions and rarefactions, when the door is opened a compression travels across the room, when the door is closed a rarefaction travels across the room
what produces a pulse? a vibration, such as a clap, causes a pulse to travel through the air, it causes particles of air to move back and forth in the same direction the wave is moving, the area where the particles are pushed together is called a compression
area where the particles are spread out is a rarefaction
what travels from one place to another? it is not the medium that is travelling from one place to another, it is the energy that travels
describe what happens when sound waves are in a tube when the prong of a tuning fork next to the tube moves toward the tube, a compression enters the tube, when the prong swings away, in the opposite direction, a rarefaction follows the compression, as the source vibrates a series of compressions
and rarefactions is produced
what does sound travel in? solids, liquids, and gases, move fastest in solids, then liquids, then gas (air), sound cannot travel in a vacuum
what does the transmission of sound require? a medium, if there are no molecules to compress and expand then there is no sound, sound can be heard from the ringing bell when air is inside a jar but not when the air is removed
what does the speed of sound depend on? the speed of sound in a gas depends on the temperature of the gas and the mass of the particles in the gas, the speed of sound in a material depends on the material's elasticity
what travels faster, light or sound? sound travels much slower than light, you see lightening before you hear thunder
what is the speed of sound in dry air? 330 m/s, 1/1,000,000 the speed of light
what conditions change the speed of sound in air? water vapor and higher temperatures increase the speed of sound in air, for each degree increase in air temperature above 0degrees C the speed of sound in air increases by about 0.6m/s
since speed of sound in a material depends on the elasticity of the material, what is elasticity? elasticity is ability of a material to return to its normal shape after a force is applied to it, sound in steel is 15 times the speed of air, sound in water is 4 times the speed of sound in air
what is sound intensity? sound intensity is objective and is measured by instruments. loudness on the other hand as a physiological sensation sensed in the brain (intensity-amplitude-amount of energy carried around the wave)
how can intensity be measured? by an oscilloscope, based on the amplitude(intensity) of the sound wave, measured in decibels (dB)
what is the amplitude or volume of a sound wave? the amount of pressure exerted by a sound source to air molecules, the higher the pressure, the harder the molecules will collide and the farther the wave will travel
what is loudness? out interpretation of intensity
describe differences in sound intensity starting with 0 at the threshold of normal hearing, an increase of 10dB means that sound intensity increases by a factor of 10, a sound of 10dB is 10 times as intense as sound of 0 dB, 20dB is not twice but 10 times as intense as 10dB, or 100 times
as intense as the threshold of hearing, a 60dB sound is 100 times as intense as a 40dB sound
important sound levels to know threshold of pain-120dB, normal speech-60dB, close whisper-20dB
describe hearing damage begins at 85 dB, depends on the length of exposure and on frequency characteristics
what does a single burst of vibration do to the ear? a single burst of sound can produce vibrations intense enough to tear apart the organ of Corti, the receptor organ in the inner ear, less intense but severe noise can interfere with cellular processes in the organ an cause its eventual breakdown
can the cells of the organ regenerate? no
what happens when an elastic object is disturbed? when any object composed of elastic material is disturbed it vibrates at its own special set of frequencies which together form its special sound, this is the objects natural frequency
what does natural frequency depend on? depends on elasticity and shape of the object, requires minimum energy to produce forced vibrations, requires least amount of energy to continue the vibration
what are sounding boards? they are an important part of all stringed musical instruments because they are forced into vibration and produce the sound
what happens when a vibrating object touches another vibrating object? a vibrating object can cause another object to start vibrating, this forced vibration can make sounds louder
how is a tuning fork an example of this? a tuning fork vibrating in the air is very faint, set the tuning fork on a table and the table top begins to vibrate,many more molecules of air are set in motion which makes the sound louder,this is the principle of sounding boards in stringed instruments
when does an object resonate? an object resonates when there is a force to pull it back to its starting position and enough energy to keep it vibrating
what is resonance? resonance is the increased amplitude caused when the frequency of a forced vibration of an object matches the objects natural frequency
what does something need to resonate? a force to pull it back to its starting position (it must be elastic), enough energy to keep it vibrating, ex. pumping a swing
what does a tuning fork need to cause another to start vibrating? a matched frequency, turning a radio dial sets the natural frequency of particular electronics to match an incoming signal
how did soldiers make a bridge collapse? soldiers marching in rhythm on a bridge set up resonance when their marching rhythm matched the natural frequency of the bridge, the bridge collapsed, tacoma narrows bridge collapsed due to wind-generated resonance
what are the differences of interference to listeners? when constructive interference occurs with sound waves, the listener hears a louder sound, when destructive interference occurs, the listener hears a fainter sound or no sound at all
can sound waves be forced to interfere? yes
when does constructive interference occur? when a compression of one wave overlaps a compression of another wave, when amplitude increases loudness increases, waves are "in phase?
when does destructive interference occur? when a compression of one wave overlaps a rarefaction of another, waves cancel each other out and loudness decreases, can cause "dead spots" in auditoriums where reflected sound waves destructively interfere with unreflected waves
how is interference used in anti-noise devices? jackhammers have microphones that send noisy sounds to microchips that create another mirror image of wave patterns which are send out of phase to earphones worn by the operator
what do transverse and longitudinal waves display? interference when they are superimposed
what happens when two tones of slightly different frequency are sounded together? a regular fluctuation in the loudness of the combined sounds is heard
what are beats? special case of interference, they are periodic variations in the loudness of sound, it is caused when two slightly mismatched frequencies are sounded together
what happens with the pattern? their interference pattern lines up in phase every so often and that constructive interference of increased loudness creates a beat, number of beats/second=frequency of wave 1-frequency of wave 2
Created by: distler



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