Chapter 3-Wave Phenomenon
(many thanks to the Physics in the Classroom Website)
Longitudinal Waves
A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction which the wave moves.
Transverse Waves
A transverse wave is a wave in which particles of the medium move in a direction perpendicular to the direction which the wave moves.
Superposition
     The principle of superposition may be applied to waves whenever two (or more) waves traveling through the same medium at the same time. The waves pass through each other without being disturbed. The net displacement of the medium at any point in space or time, is simply the sum of the individual wave displacements. This is true of waves which are finite in length (wave pulses) or which are continuous sine waves.
Beats
Reflected Pulses
A must with lots of links: Acoustics and Vibration Animations
Dan Russell, Ph.D.
The Doppler Effect
   Heard an ambulance go by recently? Remember how the siren's pitch changed as the vehicle raced towards, then away from you? First the pitch became higher, then lower. Originally discovered by the Austrian mathematician and physicist, Christian Doppler (1803-53), this change in pitch results from a shift in the frequency of the sound waves, as illustrated in the following picture.
Reflection
Thanks to: Acoustics and Vibration Animations
Dan Russell, Ph.D.
     ECHOLOCATION and how it works. Bats send out sound waves using their mouth or nose.  When the sound hits an object an echo comes back.  The bat can identify an object by the sound of the echo. They can even tell the size, shape and texture of  a tiny insect from its echo. Most bats use echolocation to navigate in the dark and find food.
     In addition to bats, echo location is used by whales, porpoises, dolphins, seals, shrews, tenrecs, oil birds, and several species of swiftlets. It is the small, insectivorous bats, the Microchiroptera, that have highly developed echo location abilities which account for 70% of all bat species.
The elaborately designed noses of echo locating bats is somehow connected to their sonar abilities but scientists have not yet figured out the exact function.
    Bats fly with their mouths open, not to look vicious, but because they are echo locating. Almost all echo locating calls are out of the range of human hearing. Humans can hear sounds up to 20 kilohertz but bats echo locate in the 9 - 200 kilohertz range. Most of the squeaks and squawks bats make in their roost is not echo location.
    If human ears could hear the echo locating of bats our nights would be very noisy. Some bats echo locate as if "shouting", operating at loud as 110 decibels or the loudness of a smoke alarm. Others echo locate by "whispering" at 60 decibels, the level of normal human conversation.
Refraction of Sound
Echos of the Civil War!
      Early morning fishermen may be the persons most familiar with the refraction of sound. Consider that you have gone out to a lake before dawn. Just as the sun rises over a cool lake, you may hear someone speak to you, saying "Good morning!". You look around and can't see anyone. You are just about at the point of questioning your sanity anyway, being out at this time of the morning, so you decide to ignore it. But the voice comes again, "Good morning". Finally you locate the other nut who has gotten up at this hour, far across the lake -- much further than you could normally hear a voice. That fisherman is aware of the early morning lake's effect on sound transmission.
     The cool water keeps the air near the water cool, but the early sun has begun to heat the air higher up, creating a "thermal inversion". The fact that the speed of sound is faster in warmer air bends some sound back downward toward you - sound that would not reach your ear under normal circumstances. This natural amplification over cool bodies of water is one of the few natural examples of sound refraction.
Thanks to Hyper Physics
Diffraction
Classic Two-Slit Experiment
OK, let's see what happens when we shine laser light through two slits and onto a wall. Press the light source button below to see the interference pattern... many thanks to Physics 2000
Interference
Constructive and Destructive Wave Interference

Take a look at the bright and dark areas in the diagram. The dark areas are areas of destructive interference. The bright areas are areas of constructive interference.

Neat Demo!
This chapter has dealt with many new concepts and lots of terminology. Be able to distinguish between many different aspects the wave nature of sound.
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