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Elevator Question

  1. Sep 19, 2010 #1
    Suppose I am standing in an elevator which is moving downwards with an acceleration exactly equal to the acceleration due to gravity. This means that I'm in a complete state of weightlessness. If I try to jump in the elevator (with feet on floor), will I be able to do so?
     
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  3. Sep 19, 2010 #2

    Pythagorean

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    Depends on how massive the elevator is. If it's too light, you'll kick it down and the top of it will smack you in the head. If you're much lighter then the elevator, you'll fly up off the floor and bonk your head on the roof. If your relative masses are in-between, you'll both move a bit and BONK somewhere in the middle. They're all equivalent in the frame that only includes you and the elevator, but different with respect to a "stationary" object (like the Earth).

    (this is all assuming you didn't think to put your hands out above you to catch the roof of the elevator as it comes hurling towards you... or you towards it.. or... well, I guess it's all relative)
     
  4. Sep 19, 2010 #3

    Danger

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    Oh, great! Thanks a bloody lot, Python! After all of these years, and who knows how many thousands of wasted dollars, you finally see fit to inform me that all I need to do to get Bonked is cut some bloody elevator cables?! I hate you.
     
  5. Sep 19, 2010 #4

    Pythagorean

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    You haven't really bonked until you've bonked in an elevator in freefall.
     
  6. Sep 19, 2010 #5

    Danger

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    As long as it ain't one of those glass-walled things; I'm terrified of heights.

    edit: Hey! Wait a second! Shouldn't a Cessna 152 count? It's not all that much smaller than an elevator, and it was definitely in free-fall.
     
  7. Sep 19, 2010 #6
    To jump up, I need to exert 'some' force on the bottom of elevator. Since I am in a state of weightlessness, I can't do that. So I think I won't be able to jump at all no matter how hard I try.
     
  8. Sep 19, 2010 #7

    Pythagorean

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    Weightlessness has nothing to do with the repulsive interaction between you and the elevator.

    Even free floating in space, you can push off your spaceship and throw things.
     
  9. Sep 19, 2010 #8
    What is the origin of repulsive interaction.Do you mean to say that we can still exert 'muscular force'?
     
  10. Sep 19, 2010 #9

    Danger

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    I'm not sure what Pythagorean is talking about. I, personally, am perfectly capable of being repulsive with no external assistance. Should my natural endeavors appear to fall short, I always carry an emergency stash of minced garlic gel-caps.
     
  11. Sep 19, 2010 #10
    Lol.
     
  12. Sep 19, 2010 #11
    Abdul, pushing your legs vertically against a freefall elevator is the same as pushing your arms horizontally against a car. The different mass of an elevator Pythagorean is talking about are analogous to different masses of the car.

    You can also look for videos of astronauts moving around in the space station. The space station is practically a falling elevator.
     
  13. Sep 19, 2010 #12

    Pythagorean

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    the repulsive force I was referring to is specifically the electromagnetic force that keeps you from passing through objects that you come into contact with. When you push against the elevator, the electrons shielding your finger molecules repulse the electrons shielding the elevator wall's molecules.
     
  14. Sep 20, 2010 #13
    Thanks
     
  15. Sep 20, 2010 #14
    The simple answer is yes. It's the ol' equal and opposite reaction thing. You will be motionless with respect to the elevator regardless of how fast it goes. When you jump, you exert a force on the floor and it exerts a force on you. Unfortunately, if you're trying to survive such a fall, the resulting acceleration in the upward direction is very small compared to your downward velocity with respect to the Earth.
     
    Last edited: Sep 20, 2010
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