# Sound Longitudinal Waves Pressure vs. Position Graph Speed of Sound Speed of Sound (cont.)

## Sound Longitudinal Waves Pressure vs. Position Graph Speed of Sound Speed of Sound (cont.)

Daynor, Jessica, Managing Editor has reference to this Academic Journal, PHwiki organized this Journal Sound Longitudinal Waves Pressure Graphs Speed of Sound Wavefronts Frequency & Pitch (human range) The Human Ear Sonar & Echolocation Doppler Effect ( in addition to sonic booms) Interference St in addition to ing Waves in a String: Two fixed ends St in addition to ing Waves in a Tube: One open end Two open ends Musical Instruments ( in addition to other complex sounds) Beats Intensity Sound Level (decibels) Longitudinal Waves As you learned in the unit on waves, in a longitudinal wave the particles in a medium travel back & as long as th parallel to the wave itself. Sound waves are longitudinal in addition to they can travel through most any medium, so molecules of air (or water, etc.) move back & as long as th in the direction of the wave creating high pressure zones (compressions) in addition to low pressure zones (rarefactions). The molecules act just like the individual coils in the spring. The faster the molecules move back & as long as th, the greater the frequency of the wave, in addition to the greater distance they move, the greater the waves amplitude. wavelength, Animation rarefaction compression molecule Sound Waves: Molecular View When sound travels through a medium, there are alternating regions of high in addition to low pressure. Compressions are high pressure regions where the molecules are crowded together. Rarefactions are low pressure regions where the molecules are more spread out. An individual molecule moves side to side with each compression. The speed at which a compression propagates through the medium is the wave speed, but this is different than the speed of the molecules themselves. wavelength,

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Doppler Problem Mr. Magoo & Betty Boop are heading toward each other. Mr. Magoo drives at 21 m/s in addition to toots his horn (just as long as fun; he doesnt actually see her). His horn sounds at 650 Hz. How fast should Betty drive so that she hears the horn at 750 Hz Assume the speed o sound is 343 m/s. 21 m/s vL Interference As we saw in the wave presentation, waves can passes through each other in addition to combine via superposition. Sound is no exception. The pic shows two sets of wavefronts, each from a point source of sound. (The frequencies are the same here, but this is not required as long as interference.) Wherever constructive interference happens, a listener will here a louder sound. Loudness is diminished where destructive interference occurs. A: 2 crests meet; constructive interference B: 2 troughs meet; constructive interference C: Crest meets trough; destructive interference Interference: Distance in Wavelengths Weve got two point sources emitting the same wavelength. If the difference in distances from the listener to the point sources is a multiple of the wavelength, constructive interference will occur. Examples: Point A is 3 from the red center in addition to 4 from the green center, a difference of 1 . For B, the difference is zero. Since 1 in addition to 0 are whole numbers, constructive interference happens at these points. If the difference in distance is an odd multiple of half the wavelength, destructive interference occurs. Example: Point C is 3.5 from the green center in addition to 2 from the red center. The difference is 1.5 , so destructive interference occurs there. Animation