Physics of Sound What is sound? Vibrations that travel through the air (or another medium) that can be heard when they reach the ear Sound may be classified as noise based on its magnitude, characteristics, duration and time of occurrence Sound Waves Transverse vs. longitudinal
Transverse wave: A wave vibrating at right angle to the direction of its propagation Longitudinal wave: A wave vibrating parallel to the direction of its propagation Transverse vs. longitudinal; 2011 Dan Russell  Transverse vs. longitudinal wave; Physics007animations  Wave Properties Frequency (f) The number of waves passing a point in a certain time A sound wave consists of a repeating pattern of high-pressure and
low-pressure regions moving through a medium Frequency units are hertz (Hz) 1 hertz = 1 wave per second f = frequency v = wave velocity = wave length T = time or period Position (y)
f = 1/T OR f = v/ T Time T Frequency Sound is classified according to its frequency and pressure
High and low hertz numbers characterize high and low tones, respectively Humans are able to perceive sounds in the range of ~20 Hz to 20,000 Hz Wave Properties Wavelength () Again f=v/ =v/f Position (y)
Distance from a particular point on a wave to the next point that is at the same height, going in the same direction Wavelength is measured in meters Position (x) Wave Properties
Amplitude (A) The distance from the center line to the top of a crest or to the bottom of a trough Measured in meters Position (y) A Time A Speed of Sound
Sound waves need to travel through a medium (for example, solids, liquids, gases) Sound waves move through various mediums by vibrating the molecules in the matter The speed of sound varies in different media (for example, solids, liquids, gases) Temperature also dictates how fast sound waves travel Sound Waves in Solids, Liquids and Gases Molecules are:
tightly packed in rigid material less tightly packed in liquid loosely packed in gas In close proximity, molecules collide with one another to propagate waves of vibrations Graphic of molecules of solid, liquid and gas 2007 Yupi666 at English Wikipedia CC BY-SA 3.0 https://commons.wikimedia.org/wiki/File:Solid_liquid_gas.jpg Sound Waves in Solids, Liquids and Gases
Sound travels faster in solids than in gases For example, sound waves move ~13 times faster in wood than in air Sound travels faster in liquids than in gases Loosely packed molecules have further to travel and take longer to collide with one another Graphic of molecules of solid, liquid and gas 2007 Yupi666 at English Wikipedia CC BY-SA 3.0
https://commons.wikimedia.org/wiki/File:Solid_liquid_gas.jpg Sound Waves in Media Recall the longitudinal wave: Transverse vs. longitudinal; 2011 Dan Russell  Sound Measurement The scale for measurement of sound pressure is called decibels (dBs) Decibels are measured on a logarithmic scale A small change in the number of decibels results
in a huge change in the amount of noise and the potential damage to a person's hearing Decibel I b ( dB) =10 log I0 When a sound increases by 10 units on the decibel scale, its loudness becomes 10 times
more powerful represents sound intensity level measured in dB Graph of the decibel function and its inverse 2010 Name, Wikimedia Commons CC BY-SA 3.0 https://commons.wikimedia.org/wiki/File:Plot_of_decibel_and_inverse.png How do people hear? The human ear translates the energy from sound waves into neurologic impulses that are heard as sound
Cutaway diagram of human ear anatomy 2003 Iain at English Wikipedia https://commons.wikimedia.org/wiki/File:Ear-anatomy-text-small-en.png Sound vs. Noise Noise is unwanted or unpleasant sound One person may hear something as sound, while another person considers it noise Sound may be classified as noise based on its magnitude, characteristics, duration and time of occurrence
The A-weighted sound levels closely match the perception of loudness by the human ear Decibel scale 2017 Department4, Wikimedia Commons CC BY SA-4.0 https://
commons.wikimedia.org/wiki/File: Decibel_scale.jpg Health Hazards/Impacts Exposure to loud noises can cause a temporary threshold shift (TTS) in hearing sensitivity or a permanent threshold shift (PTS) A noise-induced permanent threshold shift (NIPTS) is a permanent threshold shift that can be attributable to noise exposure
Health Hazards/Impacts to Students High noise levels may obstruct students recognition of teachers' speech The extra effort required to identify and remember the words may result in fewer resources available for understanding Sound Measurement Sound level meter: Commonly, a handheld instrument with a microphone
The microphone diaphragm responds to air pressure changes caused by sound waves Smart phones now have sound monitor apps Noise Meter app on smart phone 2016 Kent Kurashima and Jana B. Milford, College of Engineering and Applied Science, University of Colorado Boulder (authors) Sound Measurements Dosimetry: The use of
body-worn instruments to monitor peoples noise exposure Engineering surveys: Noise exposure monitoring Pocket dosimeter; a NMR monitoring device with three Hall-effect sensors 2010 Elia.braggio, Wikimedia Commons (public domain) https://commons.wikimedia.org/wiki/File:Pocket_Dosimeter.jpg References
 Transverse wave and longitudinal Wave. (6-second video) YouTube. Physics007animations, Sept. 2, 2011. https://www.youtube.com/watch?v=2Wlh3M2a10U  Russell, Dan. Acoustics and Vibration Animations. Longitudinal and Transverse Wave Motion. Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License  Serway, Raymond A, and John W. Jewett, Jr. Physics for Scientists & Engineers with Modern Physics. 8th edition. Belmont: Brooks/Cole Cengage Learning, 2010. Print.  Hall, Debra, and Crystal Patillo. 2.7 How does sound travel in different environments? Kenan Fellows Program, BioMusic, Learn NC, School of Education, University of North Carolina. http://www.learnnc.org/lp/editions/biomusic/6517  Friis, Robert H. Occupational Health and Safety for the 21st Century. Burlington, MA: Jones & Bartlett Learning, 2015. Web. library.books24x7.com.colorado.idm.oclc.org/toc.aspx?bookid=93068 (ebook access requires login)  Perception of Sound - Human Ear. Sound and Noise - Perception of Sound - Human Ear. Web. http
://www.epd.gov.hk/epd/noise_education/web/text/ENG_EPD_HTML/m1/intro_1.html  Kjellberg, Anders, Robert Ljung, and David Hallman. Recall of Words Heard in Noise. Applied Cognitive Psychology, vol. 22, no. 8, 2008, pp. 1088-98. Web. http://onlinelibrary.wiley.com/doi/10.1002/acp.1422/abstract
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