raj asked in Science & MathematicsPhysics · 1 decade ago

why do we hear sound when tearing a paper?

the nature of the sound and its loudness is different when we tear a wet paper.

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  • John B
    Lv 6
    1 decade ago
    Favorite Answer

    When paper is torn, the fibers vibrate as they are broken or torn apart. More importantly, the paper amplifies the sound.

    Compare the loudness between tearing paper holding it very close to the tear and tearing paper holding it at the edges.

    The water acts as a lubricant so it takes less energy to rip the paper, so less energy is released as sound. Also, the water damps the vibration, which reduces the amount of energy released as sound and prevents the paper from amplifying the sound.

  • This is an interesting question. Think about it. Why does thing have a sound? When you shatter glass, why does it make that "krrassssh" noise? When you bite into a cracker, what makes it crunch?" It's all the same thing.

    All solids are atoms arranged in an orderly manner, held together with various types of bonds. Bonds represent states of low energy which universally, is preferred. (Why this is so is why physicists are still employed.)

    Anyway, when you tear paper, what you are doing is creating a localized area of high stress and transferring energy from your arms into the bonds. They get to the point where the energy level is so high that atoms tear away from each other. The energy you pumped in now exists as two unbonded atoms. Any excess is thrown away. It has to go somewhere (energy is conserved in the universe, more or less, except a tidbit that can turn into mass), so it goes into the air. Air molecules soak it up and hand it off from molecule to molecule. Eventually, a molecule close to your ear moves, bumping into your eardrum, which you register as sound.

    Now imagine this process happening at once to billions of atoms in the paper, and billions of air molecules. Add it all up and you have a ripping noise. The sound is strictly a matter of the frequency of the air molecules' vibrations. With wet paper, the water has already broken a lot of the bonds (but in a different way, (a way that doesn't toss excess energy into the air as sound). There are probably many other factors at place, all of which involve physics in a non-ideal universe, and that has me stumped, since my work mostly revolves around an assumption of ideality. Hope you had fun reading all this; I'm pretty sure what I said was at least 90% accurate, even though, again, it is a non-ideal scenario that I'm not an expert in.

    Also, what John B said. He seems to know more about this in general than I do.

    Source(s): I'm a scientist.
  • 1 decade ago

    I have no idea, but let's analyze this very interesting question.

    First, we all agree that we normally hear a ripping sound when paper is torn apart.

    Second, sound is no more or less than air vibrating within a range of frequencies humankind can hear.

    Thus, tearing paper must create air vibrations within normal hearing range. But how?

    Clearly the ripping sound depends somehow on the surface tension across the piece of paper. This results because, as you noted, when paper gets soggy, it's ripping sound deadens or disappears altogether...depending on how soaked the paper gets.

    And, as we have seen, when paper gets really really soaked, it tends to come undone. That is, its surface tension reduces to nil and the fibers disassociate (come apart). When that happens, little if any sound occurs when the soaked paper is rend asunder.

    So here's my guess, based on the above think experiment. I hypothesize that the sound comes from fibers suddenly pulled apart and retreating toward each paper half under surface tension. That is, surface tension towards the open or edge side of the tear is zero. That follows because there is no surface beyond the edge of the tear. So the surface tension on each of the two paper sides snaps the edge fibers toward the two paper sides of the tear; making the air vibrate and creating the sound.

    As a hypothesis, this needs to be tested for validity. A series of before and after ripping tests and consequent measures of the before and after surface tensions of the paper might validate or disprove the hypothesis.

    Very interesting question, I'm interested in seeing what others answer.

    Source(s): Physics and enigneering degrees.
  • 1 decade ago

    Well think of the composition of paper it is fibers woven closely together and the tearing of fibers is what makes that sound you hear just as in the tearing of clothing or any other fiber based material

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  • 1 decade ago

    well... something to do with the vibrations, density, mass and volume....

  • John
    Lv 4
    1 decade ago

    all actions have re-actions (same goes for sound)

  • jimmy
    Lv 4
    1 decade ago

    eh its how the human body works .

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