Peoples Physics Concepts

http://www.ck12.org Chapter 11. Wave Motion and Sound

11.5 Sound

• Describe how sound is produced and how it travels through the air to then register a signal in the brain.

Students will learn how sound is produced and how it travels through the air to then register a signal in the brain.

Key Equations

T=^1 f ; period and frequency are inversely related

v≈ 331. 4 m/s+ 0. 6 T; The speed of sound in air, whereTis the temperature of the air in Celsius

Guidance

• Sound waves are longitudinal waves. Thus, the molecules of the medium vibrate back and forth in the same
  direction as the wave is traveling through. The medium for sound is normally air for humans, but sound waves
  can travel in water, metal, etc. as well.


• An object oscillating with frequencyfwill create waves which oscillate with the same frequencyf.


• The speed of a sound wave in air depends subtly on pressure, density, and temperature, but is about 343 m/s
  at room temperature.

Example 1

Describe the pressure changes in the air as a sound wave passes a given point, then explain why a very loud sound

can damage your tympanic membrane (ear drum).

Answer

As a sound wave passes a certain point, the air pressure at that point alternates between high and low pressure.

When sound waves pass into the ear, the alternating pressures cause a pressure difference on either side of the

tympanic membrane. The pressure differences between the inside and outside of the membrane cause the

membrane to move back and forth with the same frequency as the changes in pressure. What we perceive as very

loud sounds are sound waves with very large amplitudes, meaning that the differences in pressure are very large.

The larger changes in pressure could cause damage to the membrane by causing it to vibrate too violently.

Watch this Explanation

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/1842