Sound

1
Sound!

• Physics 1010
• Dr. Don Franceschetti
• April 15, 2005

2
Nature of Sound in Air

• Origin is a vibrating object, stimulates
  vibration of something larger.
• Longitudinal waves sent through air.
• Pitch corresponds to frequency 20 to 20,000 Hz,
  below is infrasonic, above is ultrasonic.
• Sound waves consist of compressions and
  rarefaction
• Energy travels while air molecules dont.

3
Media that Transmit Sound

• Any elastic material can transmit sound.
• Speed of sound in air, about 330 m/s
• Speed increases with temperature, at 20ºC, speed
  is 240m/s
• Echoes, reflection from smooth, hard surfaces.
• Echo free rooms sound dead

4
Refraction of Sound

• Sound traveling at different speeds brings about
  refraction
• Speed of sound varies with temperature under
  water.
• Submarines hide in blind spots provided by
  thermal refraction
• Ultrasound is used for imaging

5
More about sound

• Energies are very small, 10,000,000 people to
  light a flashlight bulb.
• Resonancesympathetic vibration
• Interference of sound waves.
• Beats