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If lightning can destroy trees, how come that people survive it?

  1. Apr 11, 2012 #1
    I mean, trees are a lot bigger than people, aren't they?
     
  2. jcsd
  3. Apr 11, 2012 #2

    sophiecentaur

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    Many people don't survive, of course!

    I think it must be something to do with the difference in size and the resistivity of the structures. Trees explode because the water inside them boils rapidly and produces steam. This is because the produce of Volts and Current (defined by the overall length and the resistance) - the Power Dissipated - is high enough to boil the relatively small amount of water in the tree. (Less water implies a higher resistivity)
    For an animal body, the volts are lower (it's a shorter structure and the voltage relates to the Field times the length) and the resistance is much lower (mostly water with dissolved salts). This suggests to me that there will be less actual Power involved; not enough to actually boil your insides.
    There is also the 'skin effect' which determines the depth at which a pulse of current or and AC signal passes through a conductor. It stays just on the surface of a very good conductor. I think, therefore, that there will be more current flowing through the inside of a tree than of a human.

    Otoh, plants don't have a delicate nervous system and, if they don't actually explode, they tend to stay alive and produce green shoots from some of the shattered stump. Animal hearts can just stop from the electric shock.
     
  4. Apr 11, 2012 #3
    All that is true, but trees are not always destroyed. A hot strike will explode a tree as you say, but a cool strike will set it on fire. We can survive a very small current thru the heart, or sometimes a very large current. In the band in between we are dead. They have different theories as to why that is. Depending on the actual path the lightening takes, the actual current thru the heart can be high, low, or the fatal in between. In most cases of human strikes, the human is only a small part of the path as the air around us is ionized and becomes very conductive.
     
  5. Apr 11, 2012 #4

    Drakkith

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    How often are people DIRECTLY struck by the main path of the lightning and not an "offshoot" path? Perhaps the difference is that trees commonly take the full brunt of the strike since they are taller and wider while people are usually only indirectly struck?
     
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