Physics Asked by user164656 on January 14, 2021
How can sine waves be used to describe both alternating current and sound waves? In the case of alternating current, the zero crossing represents zero current, and the waveform below the zero crossing represents current with opposite polarity. What does the zero crossing represent in sound waves? Silence? When representing a sound wave, what does the waveform represent that is below the zero crossing? When representing alternating current, the waveform below the zero crossing represents "negative current." When representing a sound wave, does the waveform below the zero crossing represent "negative sound?"
There are several parameters that can be used to represent the sound wave. The most common is acoustic pressure. This is the change in pressure above and below the equilibrium pressure. So zero acoustic pressure means equilibrium pressure which may be just atmospheric pressure for sound waves in open air.
Answered by nasu on January 14, 2021
Look at this animation showing a sound wave propagating from right to left.
(animation from Dennis Lindwall - Marine Seismic Surveys with Vector Acoustic Sensors)
In real sound waves the oscillation is not as slow as in this animation, but much faster (between $20$ and $20000$ oscillations per second).
You see there are several kinds of oscillations occurring:
Silence (i.e. no sound) means, all particles are sitting still and also the density is constant all over the place.
Answered by Thomas Fritsch on January 14, 2021
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