Transmission delay of pressure in a fluid

AI Thread Summary
Transmission delay of pressure in fluids can create differential forces on objects, particularly in compressible mediums like air. In incompressible fluids such as water, the delay is negligible, as the speed of sound is approximately 1500 m/s, making pressure changes almost instantaneous. While sound pressure waves may reach different sides of an object at slightly different times, the overall net force difference over a complete cycle is zero. In contrast, in compressible fluids, such as air, the slower speed of sound (about 340 m/s) can lead to noticeable effects. Ultimately, the impact of transmission delay depends on the specific fluid and context.
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I would like to know if the transmission delay of pressure give a differential force on an object ? Example: an object in water, we put pressure with mass over water at right at t=0s. The pressure at right is faster on the right side than the left side (d1<d2). The object seems to move with a force in water. The delay is very small but exist. Is this true ?
 

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In water, there is effectively no delay since the medium is incompressible. For something like air, which is compressible, this can happen.
 
See section on speed of sound in water in http://en.wikipedia.org/wiki/Speed_of_sound
Although the sound pressure wave may arrive at the two sides of an object at different times, if it is a sine wave, the net force difference over a full cycle is zero.
 
boneh3ad said:
In water, there is effectively no delay since the medium is incompressible. For something like air, which is compressible, this can happen.

The speed of sound in water is about 1500 m/s compared with about 340 m/s in air. Whether you think that is fast enough to ignore depends on the situation. Sonar woudn't work in a truly incompressible fluid, for example.
 
AlephZero said:
The speed of sound in water is about 1500 m/s compared with about 340 m/s in air. Whether you think that is fast enough to ignore depends on the situation. Sonar woudn't work in a truly incompressible fluid, for example.

Fair enough. I can't argue with facts.
 

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