Sound Or Can You Hear Me Now? Standards: 4d Students know sound is a longitudinal wave whose speed depends on the properties of the medium it which it propagates. 4f Students know how to identify the characteristic properties of waves; interference (beats)

Sound in General Caused by mechanical vibration Mechanical Wave Longitudinal Wave Dilations or Rarefactions Compressions V=fl, T=1/f, E ~A2 Videos of moving sound waves Question: What is the cause of all sound? Is sound a mechanical or electromagnetic wave? Is sound a longitudinal or transverse wave? Define rarefactions, compressions and dilations. What do these facts suggest about movies that have explosions and people heard while in outer space? Activities: State that sound is caused by some sort of vibration and show Laser Disk Video ____ on sources of different waves. Show other ways to make sound. Tuning fork in water glass. Strike slip of finger on glass trick. State that sound is a mechanical wave meaning it can move through solids, liquids and gases but not a vacuum. Do doorbell demo in vacuum to show sound does not travel through a vacuum. Could also show scenes from 2001 a Space Odyssey and comment on absolute quiet. State that sound is a longitudinal wave and show laser disk movie of sound traveling through a solid. Comment on how particles of material actually collide with one another. Show transparency of sound wave and point out compressions, rarefactions and wavelength. Comment how can also draw as sine wave where vertical axis is pressure.

Human Hearing Frequency = pitch Amplitude = Loudness Intensity (power/area) Human hearing is logarithmic dB scale Intensity = P/4pr2 Question: How does the human ear interpret the frequency and amplitude of a sound wave? What is the range of human hearing? What do we mean when we say that human hearing is logarhithmic? Activities: State that humans hear frequency of sound waves as pitch. High frequencies sound higher than lower fequencies. Set up oscillascope and whistle to show these different frequencies. State that humans can hear from 20-20 000 hertz. Refer to sound poster to show this. Define ultra and infra sound and discuss sources of these frequencies of sound. Mention that earthquake waves have frequency we cannot hear but other animals can and perhaps this is why they act before the quake actually occurs. State that we hear amplitude as volume with large amplitudes being louder than small amplitudes. For physics E refer them to the suppliment that has been printed out which discusses the decibel scale and its relationship to power and intensity. In general a change of 10 decibels means 10 times the energy but only sounds twice as loud. 20-20 000 Hz Sound Spectrum Age Changes Sound Spectrum Poster

Speed of Sound Speed of sound is determined by the medium 340 m/s for dry air at 20 deg C Increases with density of material Increases with temperature Increases with humidity True also of distance Questions: What is the speed of sound for dry air at 20 degrees celsius? How do humidity and temperature affect the speed of sound in air? Does sound travel fastest in a solid liquid or gas? How come? Activities: Write speed of sound in dry air at 20 degrees C is 340 m/s Use kinetic theory to explain why density affects the speed of sound. State that sound travels about5 x as fast in water and 10x as fast in rock. Discuss putting head to ground to hear calvary or touching train rail to feel train coming. Whales can also communicate long distances. Submariners go to certain depths to communicate due to waves being tunneled through layer of ocean.

Beats Interference phenomenon occuring when two sound frequencies are sounded together Variation in loudness # Beats = f1 – f2 Question: Under what circumstances do beats occur? What actually is heard for beats? What formula is used to find the number of beats? Activities: Use Soundry website and run through beat examples. Have students notice that what they are hearing is a changing of amplitude cause by two close frequencies of sound being sounded against one another. Use Xylophone keys to demonstrate above. Explain with fingers that loud areas are places where waves line up giving constructive interference and soft areas are places where destructive interference occurs. Derive formula by talking about two people with different lengths of legs walking will every once in a while be in step. To find number of times this will happen you just take the number of steps the shorter legged person took – the number of steps the longer legged person took. The difference is the number of steps they took together. http://library.thinkquest.org/19537/Inter.html

Check Question A piano tuner tightens a piano string and hears more beats than before when sounded against his tuning fork. What should the tuner do in order to get the piano in tune? Continue tightening the string Loosen the string Do nothing the piano is in tune

Other Sound Phenomenon Interference Phasing of speakers Boxing a speaker Doppler Shift Reflection Echo Problems use t/2 Thunder Problem Poltergeist Scene use t Question: What equation should be used for the echo problem? How about the thunder problem? Activities: Speaker demonstration with constructive and destructive interference Draw echo problem. Repeat with sonar problem. Boxing a speaker demo

Transmissionability Ability of material to transmit sound with small loss in amplitude Denser materials have higher transmissionability The Indian Trick The Train Trick Whale Tricks