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Breaking Glass

  1. Sep 6, 2008 #1
    I am not sure if this is the right forum to post this but I am wondering if any of you can help me?

    Say if you drop a glass bottle from the 14th of a 15 storey building and also dropped a bottle from a 1st storey of the same building, would the glass shatter the same way? i.e. what I need to know is, is would the breakage of the glass from 14th floor to ground be spread outon the ground in the same way that it would be spread out if it had just fallen from the 1st floor?

    What's the law of physics here? Is there a lay of physics? HELP!
  2. jcsd
  3. Sep 6, 2008 #2


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    Staff: Mentor

    More energy at impact will cause the smashed particles to scatter more, it would seem. The energy is related to the velocity of the bottle at impact, so depending on what the terminal velocity of the bottle is (the fastest it can go against wind resistance), you will get the same smash pattern from some height and above (because the impact velocity is the terminal velocity, and no faster). But from 1 story versus 14 stories, yes, the impact velocity will be very different, and thus the energy of the smashed particles will be different as they fly away from the impact point.
  4. Sep 6, 2008 #3


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    Staff: Mentor

    You have Newton's laws of motion, plus the concept of terminal velocity. Dropping a bottle off a 14th story bldg is probably enough to reach terminal velocity, probably around 75-90 mph. The impact shatters the glass completely and probably causes the debris to spread out pretty far.

    Dropping off the first floor may not even provide enough speed to break the bottle, depending on the type of bottle, hardness of the ground, and whether you mean dropping it from a window or the roof of a 1 story bldg. If it does break, it would be fewer pieces and they wouldn't end up as far from the impact point.
  5. Sep 6, 2008 #4


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    Staff: Mentor

  6. Sep 7, 2008 #5
    Thanks, that is a great help and I understand it!
  7. Apr 18, 2011 #6
    Re: Breaking Glass like iPhone 4

    I wonder if anybody can explain what makes glass break based on all the discussions with the Apple iPhone 4. I had the 3 for years and dropped it many times and it never broke. My daughter had hers a month and it slipped out of her hand on to our marble counter top and the glass shattered. Apple claims a much harder glass but the problem is on the 3 the glass is wrapped in a metal bezel but on the 4 the edge of the glass is exposed to impact. What I see is the initial impact (one thin line) emanating from the edge and then it travels through the face of the glass everywhere to make the "shattered" effect. Apple claims this design is better but not only is the glass exposed to impact but the unit is heavier, slipery on the sides and straight instead of rounded so it is harder to grip. Basically, I want help in proving that the exposed edge of the glass is more prone to breakage because it gives a direct molecular point of contact for the "breaking" to begin but I don't understand exactly what happens when glass breaks.
  8. Apr 18, 2011 #7
    Re: Breaking Glass like iPhone 4

    Sometimes, an unusual circumstance can exist. That is, a forced enclosure of a glass-type substrate can induce unwanted static stresses.
    Upon impact, that stressed substrate may well break easily.
  9. Apr 18, 2011 #8
    Depends on a lot of things, type of glass etc..

    I have noticed some glass (drinking glasses) actually bounce and shatter in mid air!!
    (or seem to!!).

    Complex material glass, depends on how it was cooled and hence crystal size?

    Also gonna depend how it lands.

    Generally speaking the higher the fall the wider the spread out of glass as any sideways forces will be larger.
  10. Apr 18, 2011 #9
    Re: Breaking Glass like iPhone 4

    I think thinks like scratches in the surface will weaken it. If you want to break something glass like you score a line and you can with luck break it cleanly along the line.

    It would seem obvious the exposed corner is weaker, maybe it lets the signal through easier like that, or maybe it increases revenue from re-sales when the break.

    I got a phone quite similar to a iphone but for 1/4 of the price, lower specificaction but then cheaper to replace.

    You might find this amusing - or not lol.

    Last edited by a moderator: Sep 25, 2014
  11. Apr 18, 2011 #10
    Now that I stopped laughing - still wondering in a molecular level what happens to the glass that makes it shatter when dinges in one small place on the edge? This is the composition
    Typical composition of aluminosilicate glass is 55.0% SiO2, 7.0% B2O3, 10.4% Al2O3, 21.0% CaO, and 1.0% Na2O. In the ITO coated products, no passivation layer is present. ITO is directly applied to the substrate.
  12. Apr 18, 2011 #11
    Covalent bond breakage.
    Now that's a simple and direct answer.
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