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Thread: sound of breaking brick

  1. #1 sound of breaking brick 
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    Hi physisists,
    I've a somewhat strange question:
    what if: I put a brick in a bag and throw it from a certain hight so it breaks. That will make a sound.
    but when I first break the same brick with a hammer or so, an then put it in the bag and throw it down the same hight.
    what sound will be louder?

    i ve got two theories:
    the whole brick will make more sound because there is a bigger surface to break,
    but the bag with little bricks will have more friction so more soundwaves who will add up to a louder sound..
    what do you guys think?

    greetings
    Laurent


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  3. #2  
    Forum Radioactive Isotope
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    I will guess that it will be loudest if you don't break it first.

    I think the sound will be more concentrated (but I am not a physicist).

    If you broke the brick into enough pieces it would be dust and would definitely make less sound so perhaps breaking it into 2,3,4,5 etc pieces would give a sound less than not breaking at all it but louder than if you had ground it to powder before dropping it.

    If the bag was made of a really strong material that only burst when reaching the ground at a high speed I am not sure if that would change the answer to your question.(not completely that I am sure I am right anyway)


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  4. #3  
    Forum Radioactive Isotope MagiMaster's Avatar
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    Actually, most of the sound you'd hear from throwing a brick off a building would be from it displacing the air under it as it hits the ground. The brick breaking probably doesn't add much to that. (You'd hear almost as loud of a sound if you dropped it from just under high enough to break.)

    The thing is, sound is the motion of air. While the sudden movement of the two halves of a snapping brick moves some air, most of the energy would go into the rest of the brick as heat. (That said, I'm not a physicist, so perhaps I've got a few details wrong.)
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  5. #4  
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    It also matters how the brick hits the floor. If it hits squarely on its largest face, it will make a louder sound than if the brick hits on a corner. (Anyone who has dropped a book on a hard smooth floor can attest to how loud it can be if the book hits squarely on its largest surface, which is the front or back of the book.. Also, sound is just one of the types of energy given off when a brick hits the floor and gives up its kinetic energy. There is also heat.
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  6. #5  
    Forum Cosmic Wizard
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    Quote Originally Posted by laurentvdp View Post
    ...but the bag with little bricks will have more friction so more soundwaves who will add up to a louder sound..
    what do you guys think?

    greetings
    Laurent
    If there are more that one point for the sound source you could also get crests and troughs cancelling in the sound waves.

    What would happen if you were dropping the bags of bricks into water instead. ?The fact the crushed bricks are in a bag changes things from what would happen if the broken brick was loose because the loose brick pieces would be dispersed more when they hit.

    Other than that I would suggest considering the idea of a rock dropping into water, a bag of gravel and a loose handlful of gravel, both weighing the same as the rock, dropped into a lake.
    The wave made by the solid rock and the bag of gravel should be about the same, but because the loose gravel will be dispersed over area and over time most of the waves will be small and on average will never have as great a magnitude as the single wave from the solid or baggged stone.
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