SOUND- Unit 2

Sound (researched by J.Redmond-08-23-06)Notes for Teachers of the PP&T Unit on Sound

Information provided by: http://www.decibels.demon.co.uk

Sound is produced when the air is disturbed in some way, for example by a vibrating object. A speaker cone from a hi-fi system serves as a good illustration. It may be possible to see the movement of a bass speaker cone, providing it is producing very low frequency sound. As the cone moves forward the air immediately in front is compressed causing a slight increase in air pressure, it then moves back past its rest position and causes a reduction in the air pressure (rarefaction). The process continues so that a wave of alternating high and low pressure is radiated away from the speaker cone at the speed of sound.

Information provided by: http://www.decibels.demon.co.uk

The speculation that sound is a wave phenomenon grew out of observations of water waves. The rudimentary notion of a wave is an oscillatory disturbance that moves away from some source and transports no noticeable amount of matter over large distances of propagation(wave building). The possibility that sound exhibits similar behavior was emphasized, for example, by the Greek philosopher Chrysippus (c. 240 B.C.), by the Roman architect and engineer Vetruvius (c. 25 B.C.), and by the Roman philosopher Boethius (A.D. 480-524). The wave interpretation was also consistent with Aristotle's (384-322 B.C.) statement to the effect that air motion is generated by a source, "thrusting forward in like manner the adjoining air, to that the sound travels unaltered in quality as far as the disturbance of the air manages to reach."

An important experimental result, inferred with reasonable conclusiveness by the early seventeenth century, with antecedents dating back to Pythagoras (c. 550 B.C.) and perhaps further, is that the air motion generated by a vibrating body sounding a single musical note is also vibratory and of the same frequency as the body. The history of this is intertwined with the development of the laws for the natural frequencies of vibrating strings and of the physical

interpretation of musical consonances. Principal roles were played by Marin Mersenne (1588-1648), a French natural philosopher often referred to as the "father of acoustics," and by Galileo Galilei (1564-1642), whose Mathematical Discourses Concerning Two New Sciences (1638) contained the most clear statement and discussion given up until then of the frequency equivalence.

Mersenne's description in his Harmonic universelle (1636) of the first absolute determination of the frequency of an audible tone (at 84 Hz) implies that he already demonstrated that the absolute-frequency ratio of two vibrating strings, radiating a musical tone and its octave, is as 1 : 2. The perceived harmony (consonance) of two such notes would be explained if the ratio of the air oscillation frequencies is also 1 : 2, which in turn is consistent with the source-air-motion-frequency-equivalence hypothesis.

The comparison with water waves was strengthened by the belief that air motion associated with musical sounds is oscillatory and by the observation that sound travels with a defined speed. Another matter of common knowledge was that sound bends around corners, which suggested diffraction, a phenomenon often observed in water waves. Also, Robert Boyle's (1640) classic experiment on the sound radiation by a ticking watch in a partially evacuated (partial vacuum) glass vessel provided evidence that air is necessary, either for the production or transmission of sound.

The wave viewpoint was not unanimous, however. Gassendi (a contemporary of Mersenne and Galileo), for example, argued that sound is due to a stream of "atoms" emitted by the sounding body; velocity of sound is the speed of atoms; frequency is number emitted per unit time.

The apparent conflict between ray and wave theories played a major role in the history of the sister science optics, but the theory of sound developed almost from its beginning as a wave theory. When ray concepts were used to explain acoustic phenomena, as was done, for example, by Reynolds and Rayleigh, in the nineteenth century, they were regarded, either implicitly or explicitly, as mathematical approximations to a then well-developed wave theory; the successful incorporation of geometrical optics into a more comprehensive wave theory had demonstrated that viable approximate models of complicated wave phenomena could be expressed in terms of ray

concepts. (This recognition has strongly influenced twentieth-century developments in architectural acoustics, underwater acoustics, and noise control.)

The mathematical theory of sound propagation began with Isaac Newton (1642-1727), whose Principia (1686) included a mechanical interpretation of sound as being "pressure" pulses transmitted through neighboring fluid particles. Accompanying diagrams illustrated the diverging of wave fronts after passage through a slit. The mathematical analysis was limited to waves of constant frequency, employed a number of strange devices and approximations, and suffered from an incomplete definition of terminology and concepts. It was universally acknowledged by his successors as difficult to decipher, but, once deciphered, it is recognizable as a development consistent with more modern treatments. Some textbook writers, perhaps for pedagogical reasons, stress that Newton's one quantitative result that could then be compared with experiment, i.e., the speed of sound, was too low by about 16 percent. The reason for the discrepancy and how it was resolved is discussed below (Sec. 1-4 of Pierce's book), but it is a relatively minor aspect of the overall theory, whose resolution required concepts and experimental results that came much later.

Substantial progress toward the development of a viable theory of sound propagation resting on firmer mathematical and physical concepts was made during the eighteenth century by Euler (1707-1783), Lagrange (1736-1813), and d'Alembert (1717-1783). During this era, continuum physics, or field theory, began to receive a definite mathematical structure. The wave equation emerged in a number of contexts, including the propagation of sound in air. The theory ultimately proposed for sound in the eighteenth century was incomplete from many standpoints, but modern theories of today can be regarded for the most part as refinements of that developed by Euler and his contemporaries.

Information provided by: http://asa.aip.org

Acoustics is the science of sound, including its production, transmission, and effects. In present usage, the term sound implies not only phenomena in air responsible for the sensation of hearing but also whatever else is governed by analogous physical principles. Thus, disturbances with frequencies too low (infrasound) or too high (ultrasound) to be heard by a normal person are also regarded as sound. One may speak of underwater sound, sound in solids, or structure-borne sound. Acoustics is distinguished from optics in that sound is a mechanical, rather than an electromagnetic, wave motion.

The broad scope of acoustics as an area of interest and endeavor can be ascribed to a variety of reasons. First, there is the ubiquitous nature of mechanical radiation, generated by natural causes and by human activity. Then, there is the existence of the sensation of hearing, of the human vocal ability, of communication via sound, along with the variety of psychological influences sound has on those who hear it. Such areas as speech, music, sound recording and reproduction, telephony, sound reinforcement, audiology, architectural acoustics, and noise control have strong association with the sensation of hearing. That sound is a means of transmitting information, irrespective of our natural ability to hear, is also a significant factor, especially in underwater acoustics. A variety of applications, in basic research and in technology, exploit the fact that the transmission of sound is affected by, and consequently gives information concerning, the medium through which it passes and intervening bodies and inhomogeneities. The physical effects of sound on substances and bodies with which it interacts present other areas of concern and of technical application.

Some indication of the scope of acoustics and of the disciplines with which it is associated can be found in The first annular ring depicts the traditional subdivisions of acoustics, and the outer ring names technical and artistic fields to which acoustics may be applied. (The chart is not intended to be complete, nor should any rigid interpretation be placed on the depicted proximity of any subdivision to a technical field. A detailed listing of acoustical topics can be found in the index classification scheme reprinted with the index of each volume of the Journal of the Acoustical Society of America.)

Information provided by: http://asa.aip.org

Sound is the quickly varying pressure wave within a medium. We usually mean audible sound, which is the sensation (as detected by the ear) of very small rapid changes in the air pressure above and below a static value. This “static” value is atmospheric pressure (about 100,000 Pascals) which does nevertheless vary slowly, as shown on a barometer. Associated with the sound pressure wave is a flow of energy.

Information provided by: http://asa.aip.org

Hewitt, Paul - Conceptual Physics , Prentice Hall (2006)Sound- Unit IV-Chapter 26 (Pgs. 390 to 403)26.1 - The Origin of sound26.2 - Sound in Air26.3 - Media That Transmit Sound26.4 - Speed of Sound26.5 - Loudness26.6 - Forced Vibration26.7 - Natural Frequency26.8 - Resonance26.9 - Interference26.10 - BeatsSTS - Noise and Your HealthTacoma Narrows BridgeUltrasound Imaging

Robertson, William - Stop Faking It... Sound NSTA Press (2003)Chapter 1 - Stop Children, What's That Sound"Chapter 2 - Waving StringsChapter 3 - How sound Gets AroundChapter 4 - Harmonic ConvergenceChapter 5 - Waves Do Basic Math - Adding and SubtractingChapter 6 - The Hills Are AliveChapter 7 - Listening Devices

PP&T - Activities List for Sound12.01 - Auditory System12.02 - Introduction to Sound12.03 - Resonance and Interference

12.04 - Doppler Effect

Operation Physics - Sound (Donald Kirwan et.al) 1992See Binder

Operation Primary Physical Science (Donald and Gayle Kirwan -LSU)Sound and Music

1. Sound is produced by vibrating matter.2. Sound is the propagation of longitudinal waves through

matter.3. The speed of sound varies depending on the medium through which it is traveling.4. A variety of different methods are used to cause sound vibrations in musical instruments: striking, plucking, stroking, or blowing.5. Pitch (highness or lowness of sound) is related to the

frequency of vibrations.6. Loudness is related to amplitude of vibrations, size of vibrating object, and/or number of vibrating objects.7. Musical sound has tone (harmonic content, quality).8. Resonance is the inducing of vibrations of a natural rate by a vibrating source having the same frequency. (In a like sense, interference is inducing vibrations of a natural rate by a

vibrating source having a different frequency)

Student Sound LessonsSound - Unit 22.01 - Speed of Sound

BackgroundWe will start our work on sound by working with speed, a concept you should be familiar with. In the history of sound study (sometimes called acoustics) the speed of sound took quite a while to determine. We are going to present you with two methods for finding the speed of sound in air. We say, "in air", because this is how we normally sense sound. We can definitely hear sound through other media like water or various metals. We'll work with these other media later on in the unit. We get bombarded by sound almost every minute of every day. To isolate one sound source from another and determine its speed, may pose a challenge. But challenges are the forces that move scientists to discover new things. If you already know the speed of sound in air, forget it for the time being and work on finding sound's speed through experiment.

The first activity will be done outside with a starter's pistol firing a blank round. Make sure your group takes the temperature of the air at the position where the starter's pistol will be fired. You will be taking time readings at 50, 100, 150, 200 m away from the starter's pistol. Your job will be to start the watch when you see the smoke and stop it when you hear the sound. This may take some practice and a few trials at each distance. Each lab group will take its own times and we'll compare with the other groups later, back in the classroom.

Measuring the Speed of Sound in Air Using a Starter’s Pistol

AimTo calculate the speed of sound in air by collecting and graphing the average time taken for sound to travel a systematically varied distance.

ApparatusStarter’s pistol, at least 12 ‘caps’ and ear muffs for starter/s,Trundle wheel (or measuring tape), Stop watches (x 10), Thermometer (-10 to 100 oC)

Method1. Use a trundle wheel to measure out and mark distances of 50 m, 100m, 150m, and 200m (and

beyond if possible) in an appropriate area.2. The starter stands on the zero marker, gives a pre-arranged signal to ensure that the timers are

ready and then fires the pistol.3. The students use their stopwatches to measure the time between seeing the pistol smoke and

hearing the sound.4. Repeat this procedure twice at this distance.5. Repeat all of the above steps at the other distances specified in step 1.

Analysis1. Record your individual results in the table similar to that shown below.

Air Temperature: oCdistance (m) time (s) Av. Time (s)

2. Collate the class data when you get back to class and identify and discard outliers.3. Use the class data to produce an Excel chart of time (s) versus distance (m). Time is the

dependent variable and should be plotted on the Y-axis.4. Determine the gradient of this graph and manipulate it to determine the speed of sound in air.

Questions1. What uncertainty is associated with your distance measurements? Does this vary, as the

distance gets greater? Why? Calculate the average percentage uncertainty for your distance measurements.

2. Why do you take an average of the timing data? What uncertainty is associated with your timing measurements? Does the uncertainty vary with distance? Why? Calculate the average percentage uncertainty of your timing measurements.

3. Use the average percentage uncertainties to calculate the percentage uncertainty associated with your calculated value for the speed of sound in air.

4. Why is the temperature of the air when you did the prac recorded? What effect does it have?

Conclusion (write a conclusion for the experiment)

Please note that this document is based on one prepared by Phil Noonan from St. Bedes. The original is available on the STAV-AIP Conference Proceedings 2000 CD-ROM or at www.vicphysics.org

Activity 2, finding the speed of sound in the class room with a computer and a microphone. Follow directions from the experiment write-up.

Speed of SoundCompared to most things you study in the physics lab, sound waves travel very fast. It is fast enough that measuring the speed of sound is a technical challenge. One method you could use would be to time an echo. For example, if you were in an open field with a large building a quarter of a kilometer away, you could start a stopwatch when a loud noise was made and stop it when you heard the echo. You could then calculate the speed of sound.

To use the same technique over short distances, you need a faster timing system, such as a computer. In this experiment you will use this technique with a Microphone connected to a computer to determine the speed of sound at room temperature. The Microphone will be placed next to the opening of a hollow tube. When you make a sound by snapping your fingers next to the opening, the computer will begin collecting data. After the sound reflects off the opposite end of the tube, a graph will be displayed showing the initial sound and the echo. You will then be able to determine the round trip time and calculate the speed of sound.

Figure 1

OBJECTIVES Measure how long it takes sound to travel down and back in a long tube. Determine the speed of sound.

Compare the speed of sound in air to the accepted value.

MATERIALScomputer tube, 1-2 meters long Vernier computer interface book or plug to cover end of tubeLogger Pro thermometer or temperature probeVernier Microphone meter stick or tape measure

PRELIMINARY QUESTION1. A common way to measure the distance to lightning is to start counting, one count per

second, as soon as you see the flash. Stop counting when you hear the thunder and divide by five to get the distance in miles. Use this information to estimate the speed of sound in m/s.

Microphone

1 m tube

Closed end

PROCEDURE1. Connect the Vernier Microphone to Channel 1 of the interface.

2. Use a thermometer or temperature probe to measure the air temperature of the classroom and record the value in the data table.

3. Open the file “24 Speed of Sound” in the Physics with Computers folder. A graph of sound level vs. time will be displayed.

4. Close the end of the tube. This can be done by inserting a plug or standing a book against the end so it is sealed. Measure and record the length of the tube in your data table.

5. Place the Microphone as close to the end of the long tube as possible, as shown in Figure 2. Position it so that it can detect the initial sound and the echo coming back down the tube.

Microphone

Open endof tube

Figure 2

6. Click to begin data collection. Snap your fingers near the opening of the tube. You can instead clap your hands or strike two pieces of wood together. This sharp sound will trigger the interface to begin collecting data.

7. If you are successful, the graph will resemble the one below. Repeat your run if necessary. The second set of vibrations with appreciable amplitude marks the echo. Click the Examine button, . Move the mouse and determine the time interval between the start of the first vibration and the start of the echo vibration. Record this time interval in the data table.

8. Repeat the measurement for a total of five trials and determine the average time interval.

DATA TABLELength of tube m

Temperature of room °C

Trial Total travel time (s)

1

2

3

4

5

Average

Speed m/s

ANALYSIS1. Calculate the speed of sound. Remember that your time interval represents the time for sound

to travel down the tube and back.

2. The accepted speed of sound at atmospheric pressure and 0°C is 331.5 m/s. The speed of sound increases 0.607 m/s for every °C. Calculate the speed of sound at the temperature of your room and compare your measured value to the accepted value.

EXTENSIONS1. Repeat this experiment, but collect data with a tube with an open end. How do the reflected

waves for the closed-end tube compare to the reflections with an open-end tube? It might be easier to see any changes by striking a rubber stopper held next to the opening instead of snapping your fingers. Explain any differences. Calculate the speed of sound and compare it to the results with a tube with a closed end.

2. This experiment can be performed without a tube. You need an area with a smooth surface. Multiple reflections may result (floor, ceiling, windows, etc.), adding to the complexity of the recorded data.

3. Fill a tube with another gas, such as carbon dioxide or helium. Be sure to flush the air out with the experimental gas. For heavier-than-air gases, such as carbon dioxide, orient the tube vertically and use a sealed lower end. Invert the tube for lighter-than-air gases.

4. Use this technique to measure the speed of sound in air at different temperatures. Try this by aiming a heat lamp at the tube. Record the temperature of the air inside the tube. Why not measure the air temperature around the outside of the tube?

5. Develop a method for measuring the speed of sound in a medium that is not a gas.

2.02 - Sound vibration in a medium

Background

Now that you have determined the speed of sound let's see if we can find out how sound waves are formed. You and your lab group will go from station to station to learn about sound wave propagation (creation). Take good notes and be ready to discuss what you observed from each station. After you have visited all the stations, pick an expert for your group's assigned Station(s). Your expert will explain what your group learned at that particular station. You might have to be an expert on more than one station ; determined by the number of Stations.

STATION 1

Tie the rubber tubing to a doorknob or an object that is stable and fixed. Have a lab group member hold on to the free end and try to create a wave in the tubing by moving his/her hand up and down. Move the tubing up and down faster, what do you notice. Stretch the tubing a bit and try making wave pulses, what do you notice now? Try to come up with a relationship between the number of pulses, the height of the pulses and the tension you put on the tubing. You might want to isolate tension vs. wave or pulse height and quickness of pulses vs. wave height. There are others; see what you can find out.

STATION 2

Pluck the string on the sonometer listen to the sound it makes. Now loosen the tension on the string and listen to the sound and also look at the vibration of the string. Do you notice any differences in sound or wave vibration in the string? Write down your observations. Try looser and tighter stretches and see if you can make some connection between string tension and sound. Write it down and be ready to discuss your findings with the other groups.

STATION 3

Take the slinky and have two of you group members gently stretch it. Don't over-stretch the slinky, you could put it out of commission for the other activities we will be doing with it later. Have a third member of your group pinch together 5 or 6 "slinks" (loops) near one end or the other of the slinky. Release this grouping of slinks and see what happens down the length of the slinky. Repeat this by pinching fewer than 6 or more than six slinks. Try a few different combinations and record your data. What happens to these wave group pulses as the number of slinks per pulse changes?

STATION 4

Hold a plastic ruler done on a desk or table with one end of the ruler hanging over the edge of the table (half the ruler on the table and half of the ruler hanging over the edge of the table) . Pluck the end of the ruler, gently at first and then harder. What do you notice about the sound as the ruler is plucked harder? Write down your observations.

STATION 5

You will be given a coffee can with both ends removed. A balloon has been stretched and affixed across one open end. One the outer surface of the stretched balloon a mirror has been affixed. VERY CAREFULLY have one member of the lab group aim the laser pointer at the fixed (steady, not moving) mirror so that the reflection of the laser dot hits the screen in the front of the room. Once this is accomplished, have someone speak into the open end of the can. What

happens to the dot on the screen? Repeat this with other people speaking into the can. PLEASE DO NOT LOOK DIRECTLY AT THE LASER POINTER!!!!!!!!

STATION 6

Take the two coffee cans with the string attached between them outside the room onto the lanai. Have one lab group member take one of the cans and another lab group member take the other can and carefully stretch the string between them. One can will be the listening end and the other the end spoken into. The person speaking into the can should speak with a volume that is contained in the can. Don't speak so loudly that the person on the other end can hear you directly through the air. The listener should put one ear to the can and cover the other hear with his/her hand. Pull the string tightly, but NOT enough to break the string. Try talking with the string hanging limply between the cans and record what happens. Each person in the lab group should get a chance to be speaker and a listener.

02.03 - TRANSVERSE AND LONGITUDINAL WAVES

BackgroundWe have established that sound waves are created by a vibration in a medium. If you don't understand this concept, please, ask your lab table group for help or see your teacher for extra help. When you pinched a few slinks on the slinky and released them in a packet you were modeling a compression or longitudinal wave. That's sound!!! The waves created when you vibrated a length of tubing were examples of transverse or standing waves. Those waves are like light or waves through water (the good ones to surf on). We use some vocabulary like: velocity, amplitude, wavelength () and frequency () to describe wave motion in general. With compression or longitudinal waves we use the terms: compression and rarefaction. It is impossible to talk about compression/longitudinal waves in isolation from general wave theory. We need to look at examples of both types of waves (longitudinal and transverse) and then consider the mathematical relationships related to wave theory. This may seem like a lot of stuff to deal with, but seeing how these ideas work in the real word should make things easier.

Standing or Transverse Waves

http://jclahr.com/science/earth_science/standing_wave/standwave.jpg

This is the machine you will use to study standing waves. We also will need you think about some of the properties of ocean waves you have observed. This machine helps you to see nodes and antinodes. Nodes are the places where we see a pinching or crossing over spot from one part of the wave to the next. The antinode is the place where the part of the wave is the most expanded or extended put. Here is what we mean by node and antinode:

Nodes and Anti-nodes

A standing wave pattern is an interference phenomenon. It is formed as the result of the perfectly timed interference of two waves passing through the same medium (In this case the string whirling around). A standing wave pattern is not actually a wave; rather it is the pattern resulting from the presence of two waves (sometimes more) of the same frequency with different directions of travel within the same medium.

One characteristic of every standing wave pattern is that there are points along the medium that appear to be standing still. These points, sometimes described as points of no displacement, are referred to as nodes. There are other points along the medium that undergo vibrations between a large positive and large negative displacement. These are the points that undergo the maximum displacement during each vibrational (wave cycle) cycle of the standing wave. In a sense, these points are the opposite of nodes, and so they are called antinodes. A standing wave pattern always consists of an alternating pattern of nodes and antinodes.

Where the waves cross at the horizontal line are nodes. The wave parts at the highest and lowest points from the horizontal line are antinodes.Nodes and antinodes should not be confused with crests and troughs. When the motion of a traveling wave is discussed, it is customary to refer to a point of large maximum displacement as a crest and a point of large negative displacement as a trough. These represent points of the disturbance which travel from one location to another through the medium. An antinode on the other hand is a point on the medium which is staying in the same location. Furthermore, an antinode vibrates back and forth between a large upward and a large downward displacement. And finally, nodes and antinodes are not actually part of a wave. A standing wave is not actually a wave but rather a pattern that results from the interference of two or more waves; since a standing wave is not technically a wave, then an antinode is not technically a point on a wave. The nodes and antinodes are merely points on the medium that make up the wave pattern.

The wave machine has basically, two adjustments you can make: speed, controlled by twisting the pot. stem and tension on the rotating string, controlled by adjusting the PVC arms. Since the whole device is "slip-fit" (no glue) it is easily adjusted and also easily taken apart. This, of course, has a good and bad side to it. Try different speeds and tensions and see what you can get. As always, record your data.

Compression or longitudinal wave

We will use a slinky to simulate the action of a compression (sound wave) wave. In the slinky, as in most longitudinal waves, we will have points of compression (compressed slinks) and rarefaction (relaxed or separated slinks).

The held ends are nodes and the dark, more compressed areas are antinodes. The antinodes represent places where the spring is going from fully compressed or fully extended (rarefaction).

Lay the slinky on the table or lab countertop and have one student hold the slinky at each end and pull the slinky apart gently. Have another student pinch together a few slinks near one end of the slinky or the other. Release this packet of slinks and watch the pulse going

across the slinky, what do you notice; record your findings. Try bigger slink packets and see what happens and then begin to try these packets with increased tension on the slinky. Record your findings. We will soon use tuning forks and metal rods to see what happens when they are struck while being held in the ends or other places along the rod or tuning fork.

Some terms and math relationships in sound:

I previously mentioned the terms: amplitude, wavelength, frequency and wave velocity. Let's investigate these terms.

Amplitude in an ocean wave is wave height. The higher the wave the more energy and the more noise created when it hits the reef or shore. In sound, the amplitude is how loud the sound is. The harder a violinist pushes down on the strings with the bow, the louder the sound emitted or the harder they pluck the string the louder the sound. (Try this with a guitar string). Amplitude or loudness is usually measured in dB or Decibel: Jet engine at 30m=140dB, Library=40dB or a whisper=20dB

Wave VelocityThis is how fast the wave is traveling through the medium. It's usually represented as just in the equation for waves. =Velocity will usually be in m/s

Frequency () Usually measured in Hertz (Hz) used to be called cycles per second

Wave frequency is a count of how many waves pass a point in a particular length of time. You could stand out on Magic island and count the waves that pass you in a minute or hour (that would be boring). Sound and light waves travel much faster and require electronic devices to record their respective frequencies. When you tune in an FM station, the FM stands for frequency modulation. When you tune in your AM station, AM stands for amplitude modulation.

Wavelength () Usually measured in meters (for sound anyway)

The measure of wavelength is easy in ocean waves you measure the distance between two peaks or two valleys (troughs). In a compression wave you measure the distance between two compressions or two rarefactions.

If you think of = (wave velocity equals wave frequency times wave length) as a teeter-totter or balance arm, you'll realize that if one of the three components goes up or down it has an effect on the Balance of the equation. In the following example we'll change the frequency while keeping the wave velocity the same. =330m/s (original = 10Hz, original = 33m). Let's change the frequency to 70Hz. Let's say the wave speed is fixed at 330m/s. What must the be to balance the equation.(Approx. 4.714m) It helps to think of Hz as just 1/s, so that when you divide both sides of the equation by 1/70Hz; seconds cancel out seconds and you are left in meters and that's what (wavelength) is measured in.

Think of the visual concept of equation balancing;

=

If you increase the then it should follow that needs to be smaller to balance Then it needs to change from :

To:

=

What this means is that, if you increase the number of waves per second and you wish to keep the wave velocity the same, then the wavelengths need to be shorter in order to "balance" the equation. Its all about balance!!

1. What is a sound composed of?2. What is the difference between a compression and rarefaction in a sound wave?3. Sometimes when we're watching a baseball game, say at Les Murakami Stadium, we notice that we see the ball hit the bat before we hear the sound of the ball hitting the bat. What's going on here, explain.4. If a string has an of 256Hz and the wave velocity is 340m/s, what is the wavelength () on this string? (1.328m)5. If a sound has a wave of 330m/s and a of 2m, what is its in Hz? (165Hz)6. Write a one-paragraph biography of Heinrich Hertz or another scientist who had an effect on the early development of sound theory.7. Put the following three (3) media of sound in order from best to worst conductor of sound: water, air, and brass.

Although there are different models of microphones, they all do the same job. They transform acoustical movements (the vibrations of air created by the sound waves) into electrical vibrations. This conversion is relatively direct and the electrical vibration can then be amplified, recorded, or transmitted.

The type of microphone found in most telephones is called the "carbon" microphone. It consists of a thin cylinder filled with grains of charcoal and closed by a membrane. An electric current passes through this cylinder. When a sound wave hits the membrane it compresses the charcoal grains creating a better contact and changing the electrical current.

A dynamic microphone (the type used by many musicians) operates like a miniature electric power generator. An electric vibration is created when a coil of wire moves near a magnet. The motion of the coil is caused by the incoming sound waves. In this way, the dynamic microphone scan also produces sound, only in the reverse direction: They transform electrical vibrations into sound waves.

http://www.howstuffworks.com/hearing.htm