Döppler Effect (Sound)
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Discussion
Introductory text
- how to draw waves
- how to draw waves in two dimensions
[animate]
When a source of sound is stationary (v = 0) the wavefronts form concentric circles around the source. The wavelength is the same in all directions.
[animate]
When a source of sound is in motion at a speed less than the speed of sound (v < c) the wavefronts are squashed together on one side. The waves behind the source have a longer wavelength, while those in front have a shorter wavelength. An observer behind the source would hear the sound with a lower frequency, while an observer in front would hear a higher frequency than is being produced by the source. This shift in frequency is called the döppler effect.
Summary
| speed regime |
relative speed |
mach number |
mach angle |
important concept |
|---|---|---|---|---|
| stationary | 0 | 0 | – | wavefronts |
| subsonic | < c | < 1 | – | doppler effect |
| transonic | ~ c | ~ 1 | ~ 90° | sound barrier |
| supersonic | > c | > 1 | < 90° | shock wave |
| hypersonic | ≳ 5c | ≳ 5 | ≲ 10° | ? |
Problems
practice
- Write something.
- Answer it.
- Write something else.
- Answer it.
- Write something different.
- Answer it.
- Write something completely different.
- Answer it.
numerical
- problems
Resources
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