I've been thinking about this question for some time now, and couldn't get to any conculsion.

My understanding is the following:

1) when my feet and the floor are far apart (a few centimeters), they may be approximated as electrically neutral.
(ignoring any other force between my feet and the floor)
2) When my feet is close to the floor (almost touching), then there is an electric repulsion between my feet and the floor.
This electric repulsion, in terms of energy, increases both the potential energy of my feet and of the floor that I am (almost) touching.

Now, I believe that somehow this energy dissipates, which in turn ends up in my ear as a sound.
Plus, I believe that this energy has to dissipate into air, since the sound I hear travels through the air.
Thus, I came to the conclusion that:

3) the extra electric-potential energy must be somehow transferred to the air near the collision.
Assuming little to no air is trapped between my feet and the floor, I believe that the energy has to go through the following course:
4) from the interaction between my feet and the floor, to the floor near the interaction, then to the air.
5) Plus, the transfer of energy from the floor to the air has to be 'fast'. To create some kind of pulse. It has to be a quick change in air pressure, otherwise the sound would be too soft for me to hear it (which would be tiptoeing, which generates little to no sound).

Or, maybe my understanding of sound generation is wrong, and the way the sound is generated is by me stepping on the floor, creating a pulse of pressure, which propagates as a wave through the solid (the floor).
This, in turn, makes the solid oscillate in one (or more) of its normal modes.
Then, since pressure propagates more easily through solids that through gas, the 'entire' floor oscillate in one (or more) of its normal modes, which, in turn, somehow gets transferred (while keeping the frequency) to the air, then to my ear.

My questions are the following:
A) What happens in the interaction between my feet and the ground?
B) And how does it produce a pressure-wave in the air?
C) How, on the molecular level, does the extra energy given to the floor by me stepping on it, propagates until it comes as sound to my ear?


1 Answer 1


I see you have been giving it some thought, but I think you are on the wrong track.

Sound is a pressure wave. Some regions in the wave are slightly compressed, and others are slightly less dense.

Think of how a drum produces sound. When you hit it, the membrane moves slightly down. The air just above it has more space and gets a little less dense. Then the membrane moves up. Air is slightly compressed. The membrane vibrates back and forth for a fraction of a second before coming to rest. In that fraction of a second, sound is produced.

The floor may be pretty solid, but it still can vibrate a little. It doesn't take much, especially if the vibrations spread out over a large area.

Adding to the answer.

Different materials behave in different ways when you step on them. Your steps are louder on a wooden floor than a concrete floor, and even more so than on a carpet.

Vibrations are usually the result of something springy. If you hold one end of a slinky, the other end bounces up and down. A stiffer spring will also bounce, but the size of the vibrations is smaller and the frequency is higher.

Concrete is more rigid and less springy than wood. A carpet is more springy, but is is more like a slinky. It vibrates well at frequencies so low that you can't hear them.

Nothing is perfectly rigid. Everything is made of atoms. Atomic bonds are like springs. Sometimes the springs are so stiff and strong it appears that an object is perfectly rigid. But there is always some give.

  • $\begingroup$ Your answer seems to suggest that in the limit of the floor being ideally rigid percussive sound is not possible. $\endgroup$
    – user196418
    Apr 13, 2020 at 13:48
  • $\begingroup$ That may be so, but can you comment? $\endgroup$
    – user196418
    Apr 13, 2020 at 13:59

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