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The Properties of Sound Waves
Transcript of The Properties of Sound Waves
Sound waves require a medium to travel through. This means that on the moon no sound can travel!Transmission is when sound energy pass between mediums. The wave length of the sound changes because the wave speeds up/slows down. This is because of the change in the density mediums. For example, when people are on boats you can easily hear whale sounds from far away. This is because the sound travels fast and far in the water. then it reaches the surface and the people on the boat can hear them. During this process some absorption may occur. Absorption is commonly used to sound proof rooms or anechoic rooms.
Sound is frequently absorbed or transmitted when it meets another medium, but the sound wave can also turn back on itself. This is called reflection. When a sound wave is reflected the wave length remains the same. When it hits a solid medium it's amplitude becomes inverted. The phase is shifted by (1/2)x(wave length) because of its inverted amplitude. Reflection is frequently used in auditoriums. The sound waves are reflected off of walls or roofs designed to transmit the sound of deflect it properly.
Refraction is when the sound wave travels from a faster medium into a slow medium. The sound waves turn toward the side that is slower. (Refer to Image Below) If you are camping on one side of a small lake and someone else on the other. During the day you would be unable to hear them, even though you could see them, but at night you could hear them easily. This is because the lake has cooled and the temperature change refracts the sound waves upwards.
Partial reflection and refraction occurs when the sound waves hit a boundary. Some of the sound wave reflects back while the rest refracts into the medium.
If you sit outside of a gy-
mnasium you can hear
the sounds of the people
playing. Bouncing balls and etc. The sound is muffled and quiet because only some of the sound is refracting through. If you are the gym the sound seems amplified because some of the sound waves are reflecting off of the hard walls, floor and roof
Nowikow, I., Heimbecker, B., & Bosomworth, D. (2001). More Than Meets the Ear. Physics: concepts and connections (pp. 485-500). Toronto: Irwin.
R, N. (n.d.). Sound Waves. Hyper Physics. Retrieved September 23, 2014, from http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/reflc.html
Russell, Ph.D., D. A. (n.d.). Acoustics and Vibration. <i>Refraction of Sound Waves</i>. Retrieved September 23, 2014, from http://www.acs.psu.edu/drussell/Demos/refract/refract.html
Nave, R. (n.d.). Interference of Sound. Interference of Sound. Retrieved September 27, 2014, from http://hyperphysics.phy-astr.gsu.edu/hbase/sound/interf.html#c4
Nave, R. (n.d.). Diffraction of Sound. Diffraction of Sound. Retrieved September 27, 2014, from http://hyperphysics.phy-astr.gsu.edu/hbase/sound/diffrac.html
Auditoriums also use absorption to kill the sounds in areas where it may be too intense for the listener.
Diagrams courtesy of Dr. Dan Russell, Grad. Prog. Acoustics, Penn State
Photo from Physicsclassroom.com
Photo from cnx.org
There are two types of interference, Constr-
uctive and destructive. Constructive is when
the amplitudes of the wave add together and basically create a larger wave. This is when these waves combine. Loud spots in a room can be created by two speakers. e.g.>
The other type of interference
is called destructive. This occurs
when waves that are out of phase
meet. They essentially cancel each
other out and get quiet or silent. This will create dead spots in a room. Destructive interference in commonly used by noise canceling headphones to remove any unwanted outside nose and simply listen to your music. The headphones create a sound wave that is out of phase with the sounds outside your headphones. This silences or dampens exterior noise.
Sound diffraction is extremely important it is the reason we can hear sounds around corners. Diffraction itself is the bending of waves around obstacles or the spreading out of waves through small openings. The longer the wave length the easier sound waves will bend around obstacles. For example, there is a parade in town and a marching band is playing. If you were sitting around the corner of a city block you would first be able to hear the boom of the bass drum. Whereas you could not hear the sharp notes of a flute because of its tight sound waves. Diffraction is also the reason when the door to a club is open. It sounds as if all of the sound is coming from that open doorway.