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Lifting yourself up while seated

  1. Mar 24, 2012 #1
    Why is it impossible to sit in a chair and lift it up? People can lift hugh amounts of weight so why can't they lift up the chair when seated in it?
     
  2. jcsd
  3. Mar 24, 2012 #2

    russ_watters

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    Given that you have provided no constraints, it is absolutely possible!
     
  4. Mar 24, 2012 #3
    Well I was looking for some technical explanation reallly... all I know is that it's impossible because given the force you apply to try and lift yourself, you end up pushing yourself downwards and balancing the force out?
     
  5. Mar 24, 2012 #4

    I like Serena

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    If you lift something heavy, you push the object up, while at the same time pushing the earth down.
    This way you increase the distance between the object and the earth.

    If you lift up a chair while seated in it, you push the arm supports up, while at the same time pushing the seat down.
    This means that you pull the chair apart, instead of lifting it up.
     
  6. Mar 24, 2012 #5
    Would the same explanation go with the problem, of 2 people trying to pick each other up at the same time. Why don't they levitate?
     
  7. Mar 25, 2012 #6
    Off topic, but I just have to post this:
    http://bbsimg.ngfiles.com/1/21873000/ngbbs4ca94cfa070d9.jpg [Broken]
     
    Last edited by a moderator: May 5, 2017
  8. Mar 25, 2012 #7
    Yes that explanation does work in that situation. You lift the other person up while pushing yourself down thus "pulling apart" the connection between you and the other person. Study of Newton's Third Law of Motion is extremely valuable in understanding this topic.
     
  9. Mar 25, 2012 #8
    What if both people weight 100 lbs and they both pulled up on each other with the same exact force. Which one would get lifted? Would nobody get lifted? or would they both lift?
     
  10. Mar 25, 2012 #9

    jim hardy

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    Who says they can't ?

    My neighbor used to do pullups with iron weights strapped over his shoulders.
    I suppose he could have strapped a chair to his posterior as well.....
     
  11. Mar 25, 2012 #10
    it indeed is possible, provided that you strap yourself to the chair.
    you need first make sure that your arms have the strength to lift your own weight plus that of the chair (hit the gym?)

    then get a pair of crutches, or anything that's taller than the height from the floor to where your arms are. Then just push down on the support. Chair will be lifted up with your body...
     
  12. Mar 25, 2012 #11
    depends on where you push.
    If you push anywhere on the chair itself, the forces would balance out.
    If you directly push the ground, like with crutches or something else that touches the ground but does not touch the chair, then it is possible, assuming that you are strong enough.
     
  13. Mar 26, 2012 #12

    OCR

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    Naaa, you don't need crutches, kurtlesker...

    Just grab your hair, and pull... lol

    The straps on boots, work about the same... :cool:

    http://en.wikipedia.org/wiki/Bootstrapping



    OCR
     
  14. Mar 26, 2012 #13
    If you compress a spring and wrap string around the ends where it is kept compressed, it can't propel itself! At least not when you consider the system being both the spring and the string - the forces are internal. Now cut the string, they will both be propelled, relative to each other.
     
  15. Mar 26, 2012 #14
    it's because you're sitting on it

    pay attention to what your bottom does if you go and try to lift a chair while you're sitting on it, or pay attention to what your legs feel like.

    Or go and try and pick it up when not sitting on it. You should notice that your feet push harder into the ground when you pick it up.

    stand on a scale when you try and lift something reeaaally heavy like a car. You will never actually lift the car off the ground, but you will see that the weight read by the scale increases as you try to lift the car. It's all just Newton's third law of motion.
     
  16. Mar 26, 2012 #15
    My question about the 2 people who weigh 100lbs and they both lift with the same force. Who gets picked up first?
     
  17. Mar 26, 2012 #16

    I like Serena

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    Neither.
    The forces they both apply cancel each other out.
    And if one is stronger than the other, the other will have to let go and get lifted.
     
  18. Mar 26, 2012 #17
    it doesn't matter how they do it, the force that person A applies to B in order to lift them pushes himself (A) downwards. The force that person B applies to A in order to lift them pushes himself (B) downwards.

    Since they both weigh the same, the force applied by each to the other will be equal, and thus the forces pushing each of them down will be equal to the other force trying to push them up!

    go find a friend and try it out and try and get a sense for why it doesn't work
     
  19. Mar 26, 2012 #18

    jim hardy

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    Dont you guys remember trying this when you were toddlers?

    I remember vividly at about age 3 pulling up on the seat of my pants believing i'd fly to the ceiling any second.
     
  20. Mar 26, 2012 #19

    OCR

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    Last edited by a moderator: Sep 25, 2014
  21. Mar 27, 2012 #20
    Newtons third law. Thanks for clearing that up, I think of some random things sometimes lol
     
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