What+Sound+Does

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 * Reflection -** Like all other waves, sound waves will reflect off of objects. Reflection occurs when a wave "bounces" off of a barrier and travels in another direction causing a change in velocity. The reflection of sound is known as an echo.

This video is an excellent example of how sound is reflected. As Wes shouts from the center of the gymnasium, sound waves are emitted from his larynx an travel at about 342.6(m/s) in all directions. When the sound waves reach the walls of the gymnasium they are reflected thus producing the echo that can be heard in the video.

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 * Refraction -** Refraction occurs in a sound wave (as with other waves) when sound travels from one medium to another. Because sound travels at different velocities through different mediums, the refraction of sound causes its velocity to change. The video below uses dixie cups to demonstrate what sound does when its refracted.

As the video demonstrates, Wes is unable to shout loud enough to be audible on the other side of the door. He was then given a Dixie cup that's string went above the door. This change of medium (from the air to the string) allowed Wes to get his message to Cooper and exemplified refraction.

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 * Diffraction -** Another characteristic of sound is diffraction. Diffraction in a wave occurs when that wave goes around an obstacle or through an opening and sound waves are no exception. The video below demonstrates how sound is diffracted.

The previous video was a good example of how sound is diffracted. In the video Wes shouts in the men's restroom and his voice is audible by the camera's microphone in the womens restroom. This is possible because of diffraction. When Wes shouts he again emits soundwaves from his larnyx traveling at about 342.6(m/s). Most of these waves just reflect off of the walls of the men's restroom, but some of them travel out of the lavatory entrance and continue travelling into the womens bathroom where they are picked up by the camera's mic.

The second picture shows interferece so that there is a beat frequency. a beat frequency is when there are two different sound frequencys generated and the interference causes it to sound like there is a beat because of when the destructive interference causes it to sound like nothing then the constructve interference cause it to be heard again.
 * Interference -** The following two pictures demonstrate how sound interferes. When interference occurs between two sound waves, their amplitude is either increased or decreased depending on whether the interference is constructive or destructive. There are examples of both constructive and destructive interference in the following pictures. At the places where both waves are at their peak amplitude or crest there is constructive interference, which combines the two amplitudes. Where the wave crest of one wave lines up more with the trough of the other wave there is destructive interference, and the amplitude is reduced to almost nothing.

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 * Doppler Effect -** The Doppler effect is another property of sound waves. The Doppler effect can be summed up as a change in frequency with relative motion between the source of the sound waves and the observer. The equation for this change in frequency due to the Doppler effect is as follows: f' = f ( v - v(o) / ( v - v(s) ) where f is the initial frequency being emitted in (Hz), f' is the frequency heard by the observer in (Hz), v is the speed of the sound waves through their current medium (m/s), v(s) is the speed of the the object emitting the initial frequency (m/s), and v(o) is the speed of the observer (m/s).

The Doppler effect can be heard very slightly in the above video. As Cooper pushes Wes down the hallway towards the camera and microphone, a slight change in frequency can be heard in Wes's voice, this change in frequency is really very small so its not very easy to hear. Using the equatioin given above, the overall change in the frequency of Wes's voice can be approximated. During the video Wes was moving at about 3(m/s), in this example 250(Hz) will be used as the frequency of Wes's voice and it will be assumed to be constant, finally 342.6(m/s) will be used as the speed of sound through the air.

f' = f ( v - v(o) / ( v - v(s) ) f' = 250 (342.6 - 0) / (342.6 - 3) f' = 252 ∆f = f' - f ∆f = 252 - 250 ∆f = 2(Hz)

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 * Resonance** - this occurs when one tone is create that matches the tone of another tone producing object. in this case we are using two tuning forks when one tuning fork is struck it produces a tone that tone matches the other tuning fork which causes it to vibrate and produce a sound even after the original tuning fork is dampened.