Why does a surface of an object generates sound?

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Discussion Overview

The discussion centers around the phenomenon of sound generation when a surface of an object is struck. It explores the underlying mechanics of sound production, the influence of material properties, and factors such as mass and shape on the characteristics of the sound produced.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that sound is the physical vibration of a material, which is transmitted to the brain through vibrations of the eardrums, with air or other mediums facilitating this transfer.
  • One participant questions whether increased particle vibration in hot air should lead to an increase in sound perception.
  • Another participant explains that thermal motion results in equal distribution of velocities, which may cancel out sound perception on average.
  • One participant suspects that heavier objects produce lower frequency sounds compared to lighter ones, though they express uncertainty about this generalization.
  • A later reply challenges this notion, suggesting that while it may often be true for identical substances, factors like internal energy dissipation and acoustic characteristics can influence sound frequency, as illustrated by the example of a church bell versus brick.
  • Shape is noted as an important factor in determining possible wavelengths of sound, with mass density also playing a role in the relationship between space and time derivatives in sound propagation.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between mass and sound frequency, with no consensus reached on whether heavier objects always produce lower frequency sounds. The discussion remains unresolved regarding the effects of temperature on sound perception.

Contextual Notes

Limitations include assumptions about material properties and the specific conditions under which sound is generated, as well as the complexity of factors influencing sound characteristics.

touqra
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Why do hitting a surface of an object generates sound?
 
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Sound is simply the physical vibration of a material, which is eventually transferred to the brain through similar vibration of the eardrums. Usually, that vibration is carried via air to the ears, but the same result occurs in water or directly if you have your ear against the original source. Hitting an object sets up the vibration in the first place, governed by the properties of the material. Vibrations in rubber, for instance, are damped out almost immediately, whereas something like a tuning fork can keep going for ages.
 
May I ask a stupid question regarding this. In hot days, the particles of the air are vibrating more, so shouldn't we hear a sound?
 
The distribution of velocities in thermal motion is equal in all directions. So on average (and our eardrums are averaging devices) an air molecule going one way will cancel out with another one going the other way.
 
I suspect that when I hit a heavier object, the frequency of the sound produced is always lower than when I hit a lighter object. I don't know whether this is generally true.
 
That is not strictly true, although it tends to be the case with identical substances of different mass. I suspect that it's simply because more of the vibrational energy in a large object is dissipated internally. On the other hand, the shape and accoustic characteristics of different objects can reverse the tendency. Hitting a large church bell with a hammer, for instance, will produce a higher pitched sound than hitting brick with the same hammer even though the bell might weigh a couple of tons.
 
Shape is a very important factor as that governs the possible wavelengths (OK technically all wavelengths are possible, but at least it governs the likelier wavelenths). Mass density is also important as it enters the equation in the proportionality factor between the space and time derivatives.
 

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