General knowledge

Discussion in 'Physics' started by amilton542, May 22, 2011.

  1. amilton542

    Thread Starter Active Member

    Nov 13, 2010
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    When a boiling hot plate is dipped in cold water it breaks. The hotter the plate the more the atoms vibrate, the colder the plate the less they vibrate. I have came up with two conclusions, either the excited electrons are instantley pulled back towards there atom or the atoms experience a force. My question is why does the plate break when the atoms instantley vibrate less, and why does this not hold true for metal? A blacksmith will dip red hot metal into water when the atoms are vibrating even more.
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    The temperature change is not equal. Therefore, the stresses incurred are not even..Hence the cracking.

    Many metals are more flexible and atomically dense..they cool more slowly.

    The water boiling off creates a "bubble insulation" around very hot metals.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    Simple answer, glass is brittle, metal is not.

    It has everything to do with what retched said. One side shrinks while the other side doesn't, if the material can handle the stress it survives.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    It is less of an atomic vibration problem and more of a SIZE problem

    Materials of all sorts will expand when warm and contract when cold.

    The outer surface is the first to experience any change in size. The inner portions are the last to change. The larger the change in temperature the greater the expansion or contraction. Hence the STRESS that is introduced into the material.
     
  5. samuelsun

    New Member

    Nov 3, 2010
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    Hi, its have simple answer, Glass have different properties then metal. So, in this way hot glass breaks and metal did not...
     
  6. davebee

    Well-Known Member

    Oct 22, 2008
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    I guess it's simple or not depending on how far you want to go into the physics, the details.

    But it's really not as simple as either brittleness or thermal expansion - they both are involved in the case of glass vs. metal.

    Pyrex glass is just as brittle as any other glass, but it is formulated to have very little expansion over temperature changes, so it is able to stand boiling water with no breakage.

    Metals do expand and contract, but not being so brittle, they also are able to contain boiling water without breaking.
     
  7. strantor

    AAC Fanatic!

    Oct 3, 2010
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    The same does hold true to for metal, especially if it is not cooled evenly. I used to be an amateur blacksmith. I have first hand experience on this and captured it on video http://www.youtube.com/watch?v=Z5aHi3dMl-U
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I suspect that in the case of metal and glass both, the reason for the cracking is uneven cooling. Since a plate may not be the exact same thickness the whole way through, the thinner parts will cool (and contract) at a different rate than the thicker parts. Since the crystalline structure of the plate cannot flex, it shatters. Same happens with metal to lesser degree since it has a little bit of "give" (less crystalline structure) to it, but still happens none-the-less.
     
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