www.lsmsa.edu teacher Robert Dalling's Physics Lectures (see also www.ushumans.net)
Sound and waves
Imagine a line of ten persons standing front to back. If the tenth person is shoved into the ninth person, then in turn, the ninth person will collide with the eight person who will collide with the seventh person. In turn, each person moves only for a moment and then stops as he or she hits the next person. In this way, a “people wave” moves down the line. We also see “people waves” at sporting events. Sound waves propagate in the same manner: one piece of air momentarily pushes its neighbor.
Sound is generated by vibrating objects as they push the surrounding air. For example, as a tuning fork moves left, it pushes pieces of air (atoms); as it later moves rightward, it pushes other pieces of air toward the right. This push propagates as a three-dimensional wave. The barely-visible motion of a tuning fork is more easily seen if you touch the top of water with it. The waves of air (sound) emitted from one tuning fork will cause a second tuning fork to vibrate. To see this, strike one fork and then dunk the second fork into the glass of water to see that it also had been moving.
Consider a piston within a tube. If you push the piston once inward and then stop the piston you will send a single pressure disturbance down the tube. If you repeatedly push the piston in and out then you will make a pressure wave travel down the tube. This is a sound wave. Sound is the pressure wave that consists of a series of regions of high and low density.
::::: . . . . ::::: ..... ::::: .....
A speaker creates sound as it similarly pushes on surrounding air. Our ears detect sound because ears are nothing but pressure meters. Our ears let us know when we encounter sudden changes in pressure when diving in water or rising in airplane flights. These sudden changes decrease the operation of our ears, which take a few second to recover.
If there is no air or other wiggling medium then sound does not occur. Sound does not propagate in a vacuum–despite what we sometime hear during Hollywood movies depicting explosions in space.
Demonstration
Here is a compressional or longitudnal wave on slinky. Sound waves travel as a “pushing of air” travels along. The Physics Circus team explains waves and uses a rope to demonstrate antinode jumping.
Demonstration
Stand in place at the board while holding a pen or piece of chalk in your hand. Draw a line on the board by moving your hand up and down. If you continue drawing but also walk along the board then a sine function will be drawn on the board. This shows that oscillatory, periodic, and rotational motions are closely related. For example, if a dot is painted on the edge of a spinning tire then that dot will periodically oscillate in the vertical direction while the tire rolls in a horizontal direction. Here is another animation. Notice that while vibrations are wiggles in time, waves are wiggles in space and time.
Any periodic motion is described by cosine or sine functions: y = A sin( 2πf t + φ), where y might be pressure or height or one of many other quantities. The quantity A is the amplitude of the wave. Remember that the speed of a wave is given by v = frequency x wavelength = wavelength / period
When two waves meet, the result is simply their arithmetic sum. Two waves can add constructively or destructively, depending on their relative phase. Several examples are shown here or here.
add two waves of y=sin(x) to get y=2sin(x)
subtract two waves of y=sin(x) to get y=0
add wave of y=sin(x) with y=2sin(x) to get y=3sin(x)
Student
The mathematics of waves produces art.
We have all made waves on a string or rope and seen that waves have crests and troughs; they also have wavelengths and frequencies. Aa a wave propagates along a string, the motion of a piece of the string is perpendicular to the motion of the wave. Waves on a string are said to be transverse. Here is a transverse wave. Here is a wave sent down a Shive Wave machine.
Waves
A) Waves on a string. http://phet.colorado.edu/simulations/stringwave/stringWave.swf
Slide damping to 0 and tension to high. Select “Manual” and “Fixed End.” The screen shows “wiggle me.”
1) Move the mouse up a bit and then quickly return the mouse to its starting position (stop it at its starting place). This sends a single pulse down the string. What happens to the pulse when it reflects from either end?
2) Click the reset button. Wiggle the end at the right frequency to make a single wavelength fit along the string. To instead cause two wavelengths to fit along the string, do you have to wiggle the string more frequently or less frequently? How does the speed of the pulse change if you decrease the string tension?
3) Click the reset button. Set the amplitude at 20 and the frequency at 16 and then click the “Oscillate” button. How many wavelengths fit along the string? How many fit when the frequency is doubled? What least fraction of a wavelength will fit along the string when you select fixed, loose, and no end?
B) Sound waves created by the oscillatory motion of a speaker.
http://positron.ps.uci.edu/~dkirkby/music/html/demos/PlaneWave/index.html
Click “Still Air” to see air particles colliding with neighbors within still air.
Click “temperature.” The particles bounce about but stay in place. Do they move more quickly at a higher temperature?
Click the 3rd link. Describe what it means for the air to be more dense.
Click “Sound Travelling Through Air.” Describe what you see.
Click the two “Period and Frequency” links. Describe the difference between high- and low-frequency waves.
Click “Amplitude.” What is the difference between low- and high-amplitude waves?
Click “Sound Production and Detection.” What does the tan-colored wall do to create the waves?
Click “both a source and a detector” and explain how this shows both the creation of a sound and the detection of that sound by your ear.
C) Click sound at http://phet.colorado.edu/web-pages/simulation-pages/sound-simulations.htm
Click “measure” and then “start.” Let the speaker oscillations emit 5-7 sound waves and then click “stop.” Drag the ruler to the center of the screen to measure the wavelength. You might measure the distance taken by 5 oscillations and then divide by 5 to more accurately get the length of a single wave. Compare your result to the accepted value of v = λf = 330 m/s.
C1. True or false: to increase the volume of a tone at 400 Hz heard by the listener, the speaker must oscillate back and forth more times each second than it does to produce the tone with lower volume?
C2. True or false: If the speaker produces larger fluctuations in pressure, the volume of the tone heard by the listener increases.
C3. True or false: To produce a lower pitch tone, the speaker must oscillate back and forth fewer times each second.
C4. Draw a plot of pressure versus time for a given frequency. On the same plot, draw a line representing a louder sound wave and draw a third line representing a line of twice the frequency.
Click “Two source interference,” click “audio enabled,” and then drag the happy man through the interference pattern. Can you find a place where little sound is heard?
Click “Interference by reflection” and explain what you see. Try both continuous and pulse options.
D) Doppler effect http://www.grc.nasa.gov/WWW/K-12/airplane/sndwave.html
The cricket on the left emits sound that is soon heard at the microphone, making the frequency meter show 2.5 units. The speed of the cricket is changed by moving the Mach slider, which shows the speed as a fraction of the speed of sound (330 m/s). Move the lower slider to Mach 0.5 and see the change in frequency that occurs as the cricket passes the microphone. Move the Mach slider to a value of one so that you can see the sound waves pile up. Move the slider beyond mach one to see the cone. Its angle is related through sinθ = 1/mach number = v/vs.
This animation shows waves emanating from a source and that the waves pile up when the source moves at a speed greater than the speed of sound. In this animation, move the ear toward or away from the source to see the change in received frequency. Here are two Doppler demonstrates from Wake Forest University.
E) Fourier http://phet.colorado.edu/web-pages/simulation-pages/sound-simulations.htm
How many wavelengths fit in the box when A1 is changed? When A2 is changed? A4? A8?
Click the “Math form” button to see that An sin( 2πx / λn ). Click and unclick “Sound” to hear the results. Move the sliders on the screen to match the bars shown on JC page 484 and then draw the sum shown on the screen.
F) Beats Dan Russell of Kettering University explains superposition and beats.
http://www.kettering.edu/~drussell/Demos/superposition/superposition.html
Wake Forest University demonstrates the beat frequency heard from two tuning forks that produce nearly the same frequency. Here is a graphical animation by Harvey Mudd College.
Sound waves
Transverse and Longitudinal harmonic waves
http://phys23p.sl.psu.edu/phys_anim/waves/Trans_n_Long_harmonic.avi
waves reflect and transmit portions at interfaces and boundaries
waves refract at boundaries
waves spread outward in 3D pattern from source or hole
wave motion is one aspect, as the wave passes an object it sets that object in motion briefly. the water wave is longitudinal and the objects motion is transverse. Here is a transverse wave.
energy
amplify sound of fork on table or wall, turbulence in home water pipes can be amplified noise by attached walls.
waves carry energy, e.g. break glass
energy in sound I = freq2
resonance breaks glass beakers and Tacoma narrows bridge.
Soldiers un-time when crossing bridge (learned the hard way no doubt).
Car parts resonate at certain speeds. This changes with number of passengers.
speed
v=freq x wavelength
sound speed 333 m/s while light speed is 3 x 108 m/s = 186,000 miles per hour = 7.5 trips around the earth's circumference each second. The radius f the sun is 7 x 108 m. How long does it take sun to cross one sun radius? x=vt or t=x/v =7/3 s = 2.3 seconds. If the sun went out, stopped shining, we'd see the lack of light from the point nearest us and then 2.3 seconds later we'd se no light from edge of Sun. Like a dot expanding into a circle in 2.3 seconds.
HW: how long does it take light to travel from the sun to the earth, or the earth to the moon, or the earth to a synchronous satellite orbiting at 25,000 miles above the earth's surface.
water waves = 2 flavors = gravity and ...
wave speed = sqrt(depth) so bend to arrive parallel to shore = refracted, the part of a wave farther from shore is in deeper water and so is moving faster.
deep water ------ edge of distant wave moving faster
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. . . wave turns toward slower edge
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shallow water --- edge of near wave moving slower
higher part of approaching wave has higher speed and so the wave top "crashes" over its bottom.
On hot summer desert day, the air’s temperature decreases with height above the ground and in turn, this makes light wave’s speed slows with height above the ground. The result is that a wave traveling at an angle to the ground will curve ever more upward because wave curves away from faster portion and toward slower portion. On cold winter day when the ground is colder than the air above it so both the air temperature and the wave speed increases upward, causing sound to curve toward the region of lower temperature, which is toward the ground. We can hear more distant sources on cold day then on warm day. On a cold battle day, distant cannons can be heard and not heard in alternating pattern of curve down then bounce off ground then curve down. Same for light, on certain days you might see Iceland from England (Viking diffusion) or a tower or roof top just over the horizon in summer can be visible in winter. Thunder bends upward away from warmer ground air and so is not heard beyond about 15 miles away. In the same way, a submarine can hide in a temperature profile having sound curve away from warmer water.
speed of sound = sqrt(gamma RT/molecular mass) = 330 m/s in air or 346 in warm breath within an instrument at temp of 37 °C. (1320 m/s in water 3693 m/s in copper 4650 m/s in steel) but varies with density and temp v = srqt( rho R T ). Speed of sound changes by 0.6 m/s wih each 1 C° change.
Sonar invented in 1915 look for icebergs in response to the 1912 Titanic collision. Use sonar to map ocean floor. Emit pulse, measure time to receive a reflection. If the sea floor is 10,000 m below the ship, how much time elapses between emission and reception? x=vt, so
t= x/v = (20,000 m) / (3693 m/s) = 5.4 seconds.
In a solid object v =sqrt( coefficient of elasticity/density). for a string, v = sqrt( tension/linear mass density).
Example problem 14.44 v = lambda x freq = sqrt(T/mu) where mu=linear mass density given as... get tension = 63.7 Fig Newtons.
So a warming wind instrument finds increasing speed of sound within the tube but a warming and expanding string has a decreasing tension hence a decreasing speed of sound. The pitch of warming wind instrument increases while warming string pitch decreases.
Did you know that in the 1960s, for billions of dollars the U.S. navy placed listening devices throughout the ocean to keep tabs on Russian navy. Time at which sound is received at three different listening posts locates source as in GPS device. Russian's hadn't done this and didnt know U.S. had. This allowed U.S. to know where a Russian nuclear sub had sunk. They sent a huge salvage ship to pull one up off the ocean floor. Howard Hues was paid to make a giant ship claiming to look for underwater minerals or something but it was actually a salvage ship within its hull.
Distance to thunder and height of lightning bolt:
speed of sound is 600 miles per hour = 1100 feet / s
x=vt, x=one mile = 5280 feet, t=x/v =5280 feet / 1100 ft/s = 5 seconds to go one mile. Sound speed is one mile per 5 seconds. Divide time between flash and sound in seconds by 5 to get distance in miles.
But sound not heard beyond 15 miles. so hearing thunder means lightning is within that distance.
Duration of thunder tells height of bolt. If thunder lasts 5 seconds then the ligtning was 5 sec times one-mile/5 seconds = one mile high.
If bolt is 5 miles away and 5 miles high then we get a 1:1:sqrt(2) triangle so distance to highest point of bolt is sqrt(2) times 5 miles and its duration is x=vt or t=x/v = (sqrt(2) times 5 minus 5 miles) /
time delay in seeing and hearing a gunshot to start a race
singing in shower, which is a smaller room allowing reflected sound to be heard more times rather than hearing sound once and not reflected,
frogs get in lower temp areas so mates hear lowered wavelength as if they are larger
hear noise first underwater then above it, on railroad track then above it.
Example: tap on a track and hear it with a distant ear on the track. How much sooner will the sound through iron rather than air arrive at listener a distance x=1000 m away? x=viti so ti= x/vi = 1000m / (4650 m/s) = 0.215 s, and x=viti = vata (i=iron, a=air) so
viti = vata or ta = ti vi/va = (0.215 s) (4650 / 333) = 3 sec.
HW: How much sooner will the sound through water rather than air arrive at listener a distance x=1000 away?
Differing transverse and longitudnal speeds of sound in crystal structure of metal bar. Motion better along certain directions because atoms are there while gaps are elsewhere. Tap the metal and excite the natural frquencies of the atoms in the crystal.
Fluids transmit longitudnal but not transverse sound waves. Earthquake waves move across solid Earth layers but not inner liquid layers. You can push a liquid but not shake it sideways.
Calculate pressure versus depth within the earth, P = mg/Area, but g decreases linearly with depth inside the earth. Who?
Doppler Effect
Demonstration.
Here are two Doppler demonstrates from Wake Forest University.
show concentric circles of sound from tuning fork blade then draw person moving toward or away and encountering more or fewer wave crests per second.
demo doppler effect with overhead-twirled tuning fork and cat
stick-slip
stick-slip and violins, wine glasses, chalk on board = chalk sticks then bends and stress builds until released by next slip, same for earthquakes
shock wave
http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/doppler.htm
Draw sound circles expanding from source moving at a speed less then a sound wave, and from a source moving at a speed greater than the speed of sound. As the source moves a distance vst the expanding waves move outward a distance vt. The wave front line is perpendicular to vt line, and so sinΘ=opp / hyp = vt / vst =v/vs because vt is the hypotenuse. also sinΘ=1/mach number. As a rocket rises in the atmosphere, the speed of sound decreases and the exhaust angle expands. Since PV=nRT or P = rho RT, both pressure and temperature are less as the rocket rises.
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vt . 90 .
. vst Θ .
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Sonic boom of whip whose speed increases as thickness decreases
sonic boom of jet.
Place this mach-two wind tunnel on an air compressor tank, open the valve to let the air exhaust straight out. Takes 45 seconds to empty the tank. Use Schieleirn photo technique to enhance the image of the shoch wave. Flow attains Mach one at the minimum, then as pipe expands air speeds up beyond Mach one, which is opposite to subsonic flow speed increasing with decreasing pipe diameter. See photos from Faber, Anderson, showing shock waves around bullets and space ships. Also peeling vortices off singing phone wires and highway trucks. I visited Moffet Field in CA which has a wind tunnel large enough to hold an entire airplane. Because I was experimenting with wind tunnels in my school lab the nearby wind tunnel labs were happy to have me come by. Every scientist is thrilled to find students sharing their interests and will try to snag you to work with them. College students work at nearby labs because those labs are searching for new researchers. If you want to work at a particular lab just enroll at a nearby college and hook up with a researcher at that lab.
AM vs FM
AM = 1 to 10 megahertz (my computer is 1 nanohertz = 1/100 years)
FM and TV are 100 - 1000 Mhz
tower height is 1/4 or 1/2 wavelength
sun sends out mostly red, green = 550 nm, blue. Our eyes see those colors because those are what are available. Creatures on other planets would see the available wavelengths from their own sun.
echo
echo from wall,
can measure speed of sound by standing the right distance from wall to hear the echo of a clap midway between a pair of actual claps.
whistle into a rotating fan or long picket fence. the returning echo has freq = 1 / time interval between asdjacent blades/posts.
blind people tap a cane and listen for echoes from large objects they want to avoid.
sea-floor exploration
navy sonar (hide in tempearture shadows)
bat echolocation uses 30 to 100 kHz.
bats use echo return time plus doppler effect to deduce size and distance of objects
dolphin echolocation and stunning of prey
dolphins breath voluntarily, consciously, not automatically.
dolpins hold their sick above water, done this for people also. They'll beach themselves when sick so they can continue breathing above water
Standing waves
demo standing waves on string tied to wall or hanging weights, show v = sqrt( tension/density ), get standing waves of 1/4 3/4 5/4
http://www.acoustics.salford.ac.uk/feschools/waves/string.htm
demo standing waves in soda bottle or water-filled tube (hear the change in resonant freq as a glass is filled with water--its pitch varies while filling) add alka-seltzer, organ pipes of increasing lengths have increasingly long standing waves. If you tap on the seltzer-filled water you'll hear a different tone because speed of sound is different until seltzer gone.
pour water in tube to hear changing tone from changing standing wave
Beats
Demonstration
Wake Forest University demonstrates the beat frequency heard from two tuning forks that produce nearly the same frequency. Here is a graphical animation by Harvey Mudd College.
beats from two speakers rotating past classroom
Beats. You take 60 steps per minute and your friend takes 58. Your beat freq is 2 per minute so you're both in step twice per minute or once every 30 seconds.
interference
demo two-slit interference of water waves (quantum particles too)
bounce sound off a concave dish and focus it--leads to lightwave lenses--fancy govt domed buildings and astro observatories concentrate sound at their focus
strouhal number
strouhal number gives freq of singing wires in wind, which is created by pressure changes received at our ear as vortices shed from alternating top and bottom sides of wire in wind. see these peeling from moving truck in light snow.
oscilloscope
show oscilloscope trace of different tuning forks, voices, and instruments
sum of many sounds, notice the envelope,
make A.M. transmission by varying amplitude of 1 Mhz carrier wave.
scattering
A million tree leaves reflect sound in a million directions. You can't tell where the chirping bird is sitting in the tree until it moves. Of interest in hiding from predators. Only birds and tree-dwelling monkeys can make noise with little concer of predators.
Sound from a source gets scattered by every object it encounters. Ear to ground might hear father away from a source due to fewer obstacles (boulders) in the ground than trees and bushes above the ground.
Sound scatters from objects small in comparison to wavelength as wavelength to the fourth power. So the higher pitch =shorter wavelength within a voice scatters less than does its lower pitched portion=longer wavelength. The received voice will be increasingly higher pitch after traversing greater and greater distances because low frequencies removed. Think of a distant person yelling at you past obstacles. Does their voice sound higher in frequency? (sunset red after all blue scattered, blue has higher freq -- lower wavelength -- because more energy but we see middle green best so emergency trucks are green)
total "internal" reflection of a sound wave occurs if you stand right aginst a round room having stone hence reflecting walls. The sound moving nearly tangential to wall, one inch from your nose, keeps bouncing nearly tangentially all the way around. The bouncing sound is close to the wall. Stand an inch from wall on opposite side of round room and you'll hear the whisper of a friend? at the other side of the room. Place a cloth on left edge of room to block the sound.
various sounds
Medieval trupeters learned by trial and error that the flared or rounded end disperses sound to wider angle
low freq foghorns go farther (we were lost in bay)
knuckle crack: gas bubbles build in fluid lubricating joints. When you pull the joint you increase volume and decrease pressure and the gas bubbles burst. when gas rebuilds bubbles you can crack again.
collapse of a bubble produces much more sound than the nearly silent formation of a bubble. As a stream size increases it starts making bubbles. brooks babble because of bursting bubbles.
As rice-krispies cereal becomes soggy the trapped air escapes and we hear crackling.
As ice warms, thermal stress cause cracks which can be heard.
tone of car tire over road dents, same as distance between adjacent strings within cloth. cloth riping speed determines tone heard
Ultrasound
Pressure on a piezoelectric crystal causes a voltage difference across that crystal, or a votage across the crystal compresses or expands the crystal. A varying voltage expands and contracts the crystals, sending out a sound wave.
demo wave on string bounces off inverted when meeting a heavier string. some transmits and some bounces back = reflects.
Ultrasound (career speaker Jan 23) has frequency of 20k to 100k, which is above human hearing. Might irritate some other animals. Ultrasound measures distance to object by measuring the time delay between the emmision and reception of a sound pulse. and is based on reflections from changing tissue densities. For a sound wave traveling in a material of density p1, the fraction f of perpendicularly incident sound bouncing of an encountered material of density p2 is
f = [ ( p1 - p2 ) / ( p1 + p2 ) ]2
Instead of densities, this is often expressed in terms of acoustic impedance = density times speed of sound in each material. There are tables of measured values for speed, density, and acoustic impedance in various materials and tissues.
If the sound emitted from the piezoelectric source traveled through the air before encountering the person, then a lot of that sound would bounce back. So a mineral oil having a density similar to that of skin fills the space between the source and the person. This minimizes back reflection.
A good transmitter is always a good receiver also, e.g. speakers. Car radio antennas have same shape (a wire) as radio transmitters.
The crystal sends out a pulse and then receives it back.
Ultrasound with the Doppler effect is used to measure the speed of blood flowing in veins and arteries.
Ultrasound blasts apart tumors
It also sees babies, tumors, and heart and eye disease, even sees the heart of the baby within the womb.
Energy decays exponentially as it travels through a medium E=Eoe-kx. This measn it will be heating the material. There are tables of measured absorption coefficients = k for various materials and tissues. Exponential decay is like the head light in the fog or an advertising light beam that suddenly disappears in the clouds. This absorption rate can be given in terms of a half-value thickness. To look deeper in the body, ultrasound has to amplify the return signals arriving last back at the receiver: the intensity of the last waves will be smallest.
Waves reflect most off objects larger than a wavelength. Objects of size ess than a wavelenght are not seen. The resolution of ultrasound is best at shorter wavelengths = higher frequencies. In water, a 1.2 MHz frequency has wavelength l=v/f = 1.5 x 103 / 1.2 x 106 = 1.2 mm and so sees nothing smaller than 1.2 mm in size. Higher frequencies reolve smaller objects but are more absorped.
Police radar uses the doppler effect ot determine our speed. Due to the difference in transmitted and received wavelengths. Just yesterday, a cop measured my speed this way. The speed limit was 25 mph but I told him I was dyslexic.
Auto-focus cameras measure distance using ultrsound. The elapsed time between emissionand reception of a sound wave gives the distance hence focuses the lens at the right range.
A stone is dropped into a well and the splash is heard t3 seconds later. How deep is the well? h=1/2gt2 so t to fall = sqrt(2gh) and the time for sound to return is h=vt or t=h/v and total time t3 = t1 + t2 = sqrt(2h/g) + h/v. Solve for h=18.5 meters for t = 2 sec.
human speech
We produce sound within the lumpy adam's apple. Someone should ask the internet where that name came from. Some piece of tissue is set vibrating as air pressure and speed varies under the influence of Bernoulli. When tighten a muscle to change frequency through v = sqrt( tension/linear mass density). Male voices around 125 Hz and female around 250 Hz. Singing ranges from a low C = 64 Hz = bass to a soprano of 2048 Hz.
Nose influences sound too. As we plug our nose to hear. Plug your ears and talk and you'll hear yourself just through the bones of your head.
Have you heard the throat singers of Tuva. Sometimes we hear someone talk or sing out of their throat. A person whose larnx has been removed talks by controlled burping.
Whale, bird, wolf, primate singing communicate with group members or to attract mates, or to keep others away, e.g. as do lone-hunting coyotes. There is a group of primates in which family members sing to communicate with each other through the day.
animal produce frequency proportional to 1/size from nats, misquiotes, fly wings, then mice to dogs to bears.
A sound energy of a two-second sentence is 10-5 Joule or 10 micro Watts. The energy needed to talk for one year equals the energy in a cup of boiling water. Vowels require 680 times the power of a consonant. Most animals have a straight line from belly through throat and then teeth. When hominids stood we got a 90-degree angle at our teeth and may have then began to make consonants. Chimps make 'e' and 'o' vowells, not consonants.
standing waves in our mouth resonator.
demo helium and sulpher hexaflouride breaths (if using hydrogen you'll explode like the Hindenburg) People staying for extended times in deep sea labs put helium in air and so talked funny--until they got used to it.
Two people don't use the same tongue and lip movements to produce the same letters or sounds. Its not a one to one relation. Each letter can be produced with lots of lip and tongue combos.
resonance in sperical tubes or seashells too=hear the "ocean" noise as resonant frequency plucked from passing sounds.
We effortlessly speak after practicing for hundreds of hours. Same for walking, running, bicycling, adding, reading, driving, catching, batting, chess, physics... That's all there is to it.
Neurologists measure neuronal connections increasing in number as we learn a task. These neurons are specialized to that taks, and many other tasks. Your entire skin is mapped onto brain surface, the map has the same shape as your fingers and such. Gaining adeptness at playing the trumpet increases the relative size of those finger's brain area. Draw a hand with enlarging fingers.
Human hearing:
We hear in the range 20 - 20,000 hz, except everyone varies a bit and old people often can't hear above 10k. Our ears are most sensitive at 1000 - 10,000 Hz. Our heart (0-150 Hz) and lungs (150 - 1000 Hz) make sounds in low frequencies that we don't hear so well (or we'd drive ourselves nuts.) There's a rumour that your dog hears your heartbeat and so detects heart rate extremes.
Range in intensities of faintest to most bearably-loud sound is 10-12 to 1 W/m2 corresponding to the motion of air atoms about their equlbrium point of 10-100 to 10-5 meter. This displacment makes hairs wiggle within our inner ear. The pressure of a sound wave is 10-5 N/m2 remember air pressure is 105 N/m2. Sound intensity ratios are measured in Bels after Alexander Graham Cracker Bell, who invented snack food while doing research in sound and hearing.
gain 6-8 dB by cupping your hands behind your ears, try it. It works to make movable ears in animals, as we've seen our dogs and cats do. some people can wiggle their ears--even one at a time for the amusement of all. Ears grow larger throughout life? Bones within the ears of a fetus are adult size and so can hear if the brain is listening.
Wiggling hairs within the corti within the chochlea activate nerves interpreted by the brain. A fish gill became its ear. Passed through succeeding animals. Mammals have hair. No hairs within ears of other animal types? A spider body detects web vibrations as prey are caught.
human ear distinguishes sounds arriving 0.05 seconds apart. This corresponds to x=vt=330 x 0.05 = 16.5 meters apart.
party effect, we can steroscopically pick out a nearby voice until it is drowned by the backround of many other voices. At this point, everone begins shouting. If you tape record the party then the stereo info is lost and all voices are indistinguishably blurred.
Our own voice is heard through the air and the bones of our head, which transmit more low frequency than air. bones transmit sound, we hear ourselves differently than do others. Birds hear and monitor the sound they are making. Their brains take into account the time delay of sound moving through their bones.
We steroscopically determine direction of sound souce from differences in arrival times, and by differences in intensity of wavelengths (shorter than your head diameter) at one side or other, and by phase differences of longer wavelengths.
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Nature 420, 475 (05 December 2002); doi:10.1038/420475a
Animal communication: Tree-hole frogs exploit resonance effects
BJÖRN LARDNER* AND MAKLARIN BIN LAKIM†
* Division of Amphibians and Reptiles, Field Museum of Natural History, Chicago, Illinois 60605, USA
† Research and Education Division, Sabah Parks, PO Box 10626, 88806 Kota Kinabalu, Sabah, Malaysia
e-mail: bjorn.lardner@zooekol.lu.se
Animal mating calls that exert a comparatively high sound pressure propagate over greater distances and generally have greater attractive power. Here we show that calling male Bornean tree-hole frogs (Metaphrynella sundana) actively exploit the acoustic properties of cavities in tree trunks that are partially filled with water and which are primarily used as egg-deposition sites. By tuning their vocalizations to the resonant frequency of the hole, which varies with the amount of water that it contains, these frogs enhance their chances of attracting females.
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Problem HRW 17.66 a) in still air.
Vs = Vsource = 30.5 Vd = Vdetector = 30.5
----→ ██ ←---- ██
The source emits sound that hits the detector and is Doppler shifted to f'. The detector then acts as a source but emits at the shifted frequency f'. The sound is again Doppler shifted when received back at the source. Rather than doing this as a two step problem, it works to combine it into one using
f' = f ( v + vd ) / ( v + vs )
The source is moving toward the detector and this wants to increase f', which happens when the denominator is reduced. We choose a minus sign for vs.
The detector is moving toward the source and this wants to increase f', which happens when the numerator is increased. We choose a plus minus sign for vd and have
f' = 500 ( 343 + 30.5 ) / ( 343 - 30.5 ) = 598 hertz donuts
b)
Vs = Vsource = 30.5 Wind to left Vd = Vdetector = 30.5
----→ ██ ← ←---- ██
Relative to the wind that is moving to the left, the detector is moving at speed vd = 0 and
the whistling train is moving at speed vs = 71 m/s. so we have
f' = 500 ( 343 + 0 ) / ( 343 - 71 ) = 608 hertz a lot
c)
Vs = Vsource = 30.5 Wind to right Vd = Vdetector = 30.5
----→ ██ → ←---- ██
Relative to the wind that is moving to the right, the detector is moving at speed vd = 71 and
the whistling train is moving at speed vs = 0 m/s. so we have
f' = 500 ( 343 + 71 ) / ( 343 - 0 ) = 589 hertz terribly
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