Why does a drip of water into water make a noise?

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Discussion Overview

The discussion revolves around the phenomenon of sound produced when a drop of water impacts a body of water. Participants explore the mechanisms behind the sound generation, the transformation of energy involved, and the comparison of this event to other sound-producing impacts, such as a hammer striking a surface. The scope includes conceptual and technical explanations related to fluid dynamics and sound wave propagation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants inquire about the nature of the 'gloop' noise and the energy transformations that occur when a drop impacts water, questioning how this energy couples into sound waves in air.
  • One participant draws a parallel between the sound produced by a water drop and that produced by a hammer hitting a surface, suggesting a common underlying mechanism.
  • Another participant references high school physics, explaining that collisions create vibrations that propagate as sound waves in the surrounding medium.
  • A more advanced perspective is provided, mentioning the Navier-Stokes equations and how they describe pressure waves in air when disturbed by vibrations from impacting bodies.
  • Concerns are raised about the nature of waves in water, noting that water's incompressibility leads to surface waves rather than bulk oscillations, and suggesting a low frequency cutoff due to viscosity affecting sound propagation.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms of sound generation and the nature of wave propagation in water, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

Participants mention various assumptions regarding the properties of water and air, the nature of sound waves, and the mathematical frameworks applicable to the discussion, which remain unresolved.

Who May Find This Useful

This discussion may be of interest to those studying fluid dynamics, acoustics, or anyone curious about the physics of sound generation in liquids.

cmb
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What is the 'gloop' noise; what actually makes the energy noise (from gravitational/kinetic into ... what transformation?), how is that transformed energy then coupled into a propagating wave in air?

Further, whatever 'that' is, is it the same for an ocean wave, just godzilions of little drops all making the same noise close together in time and space, and if one could separate them out then the ocean would be one drip noise after another. Or something else?
 
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cmb said:
What is the 'gloop' noise; what actually makes the energy noise

A Q back at you ... why is a sound made when a hammer hits something ?

The reason is the same
 
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In terms of high school physics the collision of two bodies, creates vibration of the molecules on the two colliding surfaces and these vibrations pass into the surrounding air and form the sound waves.

In terms of graduate physics, Navier -Stokes equations which the air obeys as a fluid medium, have as solutions pressure waves in the medium when the medium (air in this case) is disturbed by the motion/vibration of other bodies.
 
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The hammer and anvil will vibrate because the materials they are made of are elastic and there is a bulk oscillation of volume once struck, leading to oscillations normal to the surface.

I understand that water is incompressible and that any waves that would carry away energy exchange to be surface waves, not bulk volume oscillations.

I could agree that some waves might be possible, but surely there would be quite a low frequency cutoff due to the viscosity of the water and its inability to couple the energy effectively to air, the amplitudes would be negligible for the spectrum of the 'plop' in the multi kHz range.
 

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