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I was wondering

  1. Oct 6, 2005 #1
    I'm not a studying physicist or anything else, but in my spare time I often sit and ponder the why and wherefore of things. Today's conundrum is: "Why don't massive or miniscule energy expenditures on the macroscale affect things on the atomic or subatomic scale."

    Everyday I use a knife or run across a sidewalk. Why don't these actions cause atomic or subatomic changes? When demolitions companies explode mountains or buildings, they don't worry about inadvertently triggering a nuclear blast. What forces allow atoms to bang about so stressfully without breaking the internal bonds?
     
  2. jcsd
  3. Oct 6, 2005 #2

    Astronuc

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    Staff: Mentor

    The strength between atoms is quite large and to melt or vaporize a solid material requires enourmous quantities of energy.

    Using a knife or walking over the sidewalk does affect some atoms, but so few that one would not be aware.

    In many solids of metals or ceramics, atoms and molecules are arranged in order crystal structures, although under special considitions, and amorphous (non-crystalline) structure may exist (e.g. glass). The crystals are arranged in grains, and the grain sizes are on the order of microns (10-6 m).

    Even the grains are strongly connected by the bonds between atoms on their surfaces. When an explosive detonates the energy may brake the weakest bonds, so materials break in pieces consisting of many grains.

    Now in an explosion, the solid materials closest to the explosion may indeed vaporize and melt. However, the energy of the explosion rapidly dissipated according to roughly 1/r3, so as the explosion progresses, the energy density drops dramatically, and so the local energy quickly drops below the levels required to vaporize or melt, but instead the adhesion between grain surfaces is disrupted.

    Nuclear explosion require very special conditions, which promote the fissioning of particular atoms. The nuclear forces holding the nucleus together are much, much stronger than the chemical forces hold atoms together, so a chemical explosion will not cause a nuclear explosion.
     
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