Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How fast can lightning change direction?

  1. May 8, 2005 #1
    Does lightning mainly just move in a straight line or can it change really quickly? Can it move around objects, like something that's not a good conductor, to get to something that is?
  2. jcsd
  3. May 8, 2005 #2
    OHh I also wonder why lightning doesnt propogate in a straight line ... but in a zigzag type of path. Is it because it chooses the path that is least resistive ?
  4. May 8, 2005 #3
    I'll take a whack at this question for you. The lightning choses the path of least resistance so it will zig zag around less conductive air to get to the ground easier. On the topic of changing direction: It obviously changes direction quickly but I only know that because I observe it. I have no information to back this up.
  5. May 10, 2005 #4
    So does anyone know for sure?
  6. May 10, 2005 #5
    Very complicated

    Well, there's a couple of things going on. It is true that lightning travels along the path of least resistance. However, before there is the main stroke of a lightning bolt, there are hundreds of leader tracks- low current short arcs- that "feel out" the local ionization, looking for a path of low enough resistance to initiate an arc. Any contaminant in the air (water vapor, dust, pollutants) that happen to be in the way of the arc provide a lower resistance than air alone. Plus, as the arc progresses, the air gets super heated - creating an ionized path as it goes. This ionized path is subject to both the eddy currents in the air and the magnetic field of the earth. Plus, the arc itself has a strong magnetic field. Plasma in a magnetic field has very complicated motion, and chaotic paths are not entirely uncommon.

    So to answer your question, I can't imagine that a lightning bolt would ever be straight, what with all the different things going on at once. :smile:
  7. May 10, 2005 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Keep in mind that a lightning is similar to an arcing or a discharge. The path that a lightning takes is very complicated due to a number of factors, such as density of the medium, polarizability, charge distribution, etc. Air in itself does not have a uniform density over a large distance (that's why we have winds). So this makes the path even more complicated.

    Note that this isn't unique just for lightning. Arcing in a medium also does not follow a straight line path. In fact, it can be downright twisted since it depends on grain boundaries, defects, variation in density, etc. To illustrate this, I have a recent SEM image that I took of a ceramic of MgCaTi compound in which an electrical breakdown occured right at the butted joint. You can see the tracks made by the arc and they look like "wormholes".


    Attached Files:

    • mct.jpg
      File size:
      81.3 KB
  8. May 14, 2005 #7
    Thanks, ZapperZ. I don't get everything you said, though. :P
    Are there any easy to understand examples of lightning changing direction quickly?
  9. May 14, 2005 #8
  10. May 14, 2005 #9
    According to an article in the latest issue of Scientific American, authored by Joseph Dwyer (researcher in Florida), the cause of lighting is much different than previously thought.

    In brief: Dwyer found copious X-ray production that he states could only be generated by high-energy electrons he calls “runaway electrons”. The x-rays are not produced during the lighting flash, but during the “leader” period preceding the flash. The underlying cause of the energetic electrons is cosmic radiation that initiates a chain reaction of free electrons. The electrons must be accelerated by a 200,000 volt per meter field to reach energies sufficient to generate x-rays. Apparently accelerated electrons, not the presumed “electrons taking the path of least resistance”, create the leader. His sensors have detected x-ray production by the leader within a few meters of the ground.
  11. May 15, 2005 #10


    User Avatar
    Gold Member

    A most interesting article; I was about to recommend it myself. That runaway electron effect seems as if it should have some practical uses if it can be harnessed. (Maybe a better Taser? :biggrin: )
    Kidding about that, but some new stuff regarding high energy discharges could help with other areas of research perhaps, such as in plasmas or materials science.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook