Doppler Effect (Sound)

Summary

• Drawing sound waves
  • One dimensional technique
    • Sound waves can be drawn as a pressure-time or pressure-distance graph.
    • Sound waves are still longitudinal waves despite the fact that this technique makes them look like transverse waves.
  • Two dimensional technique
    • Sound waves can be drawn as wavefronts.
    • Wavefronts are the locus of all points in space with the same phase.
    • The wavefronts from a stationary, point source of sound are concentric circles.
    • The wavefronts from a moving, point source of sound are circles that are positioned closer together in front of the source and farther apart behind the source.
• The Doppler effect…
  • is the apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer.
  • applies to all types of waves.
  • increases the frequency of a wave (raises the pitch of a sound wave) when the source moves toward the observer.
  • decreases the frequency of a wave (lowers the pitch of a sound wave) when the source moves away from the observer.
• Animations