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Evading lightning strikes

  1. Jun 24, 2012 #1
    I'm not sure if this question belongs here or in the classical physics section. So please forgive me if it is in the wrong place.

    My question is can a lightning strike, that originates from the sky directly above and unto a grounded target, be evaded with speeds less than the speed of the lightning itself?

    For instance, let's say the instant lightning from the clouds forms in order to strike a target directly below it the target moves. Can the target actually evade the strike with sufficient speed but less than the speed of the lightning itself? If so then how fast (in average speed) move a target be traveling if say the lightning is formed about 4000meters directly above the target?
     
  2. jcsd
  3. Jun 24, 2012 #2

    Danger

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    I've heard from people who were in close proximity to strikes that they picked up a charge that made their hair stand up in advance of the strikes. That would indicate to me that the warning, if recognized as such, would allow the potential victim to beat heat in any direction away from ground zero.
     
  4. Jun 24, 2012 #3
    But can they? How fast must they go in order to evade the strike?
     
  5. Jun 24, 2012 #4

    davenn

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    Yes, I have heard that too from a couple of my fellow storm chaser friends. The problem in the panic you wouldnt know if you were getting closer to ground zero or further away :eek:

    @ h1a8 .... the lightning discharge is going to cover that ~ 4000 metres ... give or take a bit, in a few milliseconds.
    How far can you run in say 5 milliseconds ?
    I would hazzard a guess at not far :tongue:

    cheers
    Dave
     
  6. Jun 24, 2012 #5

    DaveC426913

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    You must understand that lightning is not shooting like a bullet at a target.

    The connection between cloud and ground actually occurs before the lightning strike. The lightning strike just follows the path of least resistance.

    The evade a bolt of lightning, you must "break" the connection.


    This is a way over-simplified explanation, only intended to clarify that lightning bolts don't shoot like bullets.
     
  7. Jun 24, 2012 #6
    Thanks! I knew that lightning doesn't act like a bullet. Otherwise I could easily calculate the minimum speed with ease using basic algebra.

    The problem is that, because of the connection, lightning tends to follow and branch off (multiple strikes). There is definitely a minimum speed needed to evade the lightning strike from above. There is no question about that really. The actual speed is really the question, and a highly complicated one at that, unless you think that lightning will forever chase you, even laterally.
     
  8. Jun 25, 2012 #7

    Danger

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    My only thought would be to dive into the nearest car. Aside from a nice cave, there's no better place to be than in a Faraday cage.
     
  9. Jun 25, 2012 #8

    Bobbywhy

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    h1a8, Your question about moving away to avoid a lightning discharge seems difficult to answer. There are many types of lightning, the most common is cloud-to-ground. Please read this excerpt from Wiki and perhaps your question will be resolved:

    Leader formation and the return stroke

    As a thundercloud moves over the surface of the Earth, an electric charge equal to but opposite the charge of the base of the thundercloud is induced in the Earth below the cloud. The induced ground charge follows the movement of the cloud, remaining underneath it.

    An initial bipolar discharge, or path of ionized air, starts from a negatively charged region of mixed water and ice in the thundercloud. Ionized channels of the discharge are known as leaders. The positive and negative charged leaders, generally a "stepped leader", proceed in opposite directions. The negatively-charged one proceeds downward in a number of quick jumps (steps). About 90% of the leaders exceed 45 m (148 ft) in length, with most in the order of 50 to 100 m (164 to 328 ft).[29]

    As it continues to descend, the stepped leader may branch into a number of paths.[30] The progression of stepped leaders takes a comparatively long time (hundreds of milliseconds) to approach the ground. This initial phase involves a relatively small electric current (tens or hundreds of amperes), and the leader is almost invisible when compared with the subsequent lightning channel.

    When a stepped leader approaches the ground, the presence of opposite charges on the ground enhances the strength of the electric field. The electric field is strongest on ground-connected objects whose tops are closest to the base of the thundercloud, such as trees and tall buildings. If the electric field is strong enough, a conductive discharge (called a positive streamer) can develop from these points. This was first theorized by Heinz Kasemir.[31][32]

    As the field increases, the positive streamer may evolve into a hotter, higher current leader which eventually connects to the descending stepped leader from the cloud. It is also possible for many streamers to develop from many different objects simultaneously, with only one connecting with the leader and forming the main discharge path. Photographs have been taken on which non-connected streamers are clearly visible.[33]

    Once a channel of ionized air is established between the cloud and ground this becomes a path of least resistance and allows for a much greater current to propagate from the Earth back up the leader into the cloud. This is the return stroke and it is the most luminous and noticeable part of the lightning discharge.

    http://en.wikipedia.org/wiki/Lightning
     
  10. Jun 25, 2012 #9

    PhanthomJay

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    There is a difference between outrunning a lightning strike and outrunning the voltage gradient that builds up prior to the strike that causes your hair to stand on end.

    In the first case, forget about running or crouching and hope that in those few milliseconds the lightning finds a better path of least resistance to ground at least oh say 200 feet (60 meters) away from you.

    In the second case, if a Faraday cage is not nearby, assume lightning position immediately....crouch down low on soles of feet, click those heels together, block your ears, and I wish you well, my friend.
     
    Last edited: Jun 25, 2012
  11. Jun 26, 2012 #10

    davenn

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    Had to do that a few times, when I have been out of the car taking storm photos and a big strike hits a couple of hundred metres away. That has me diving for cover real fast

    Have yet to prove the effectiveness of the car as a Faraday cage. But it has proved effective in avoiding being hit by large hailstones :biggrin:

    Dave
     
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