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Question about Friction

  1. Sep 7, 2015 #1
    I have heard that if there were no friction between a person walking and the ground, the person would just walk in place, like a cartoon character. If this is true, then I am a bit confused, though: How would the person just walk in place and not just slip and fall if there is no friction? Someone help me out here.
     
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  3. Sep 7, 2015 #2

    sophiecentaur

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    How do you walk and control your position when standing up? You push your foot backwards / sideways. If there is no friction between your sole and the floor then that will have no effect. You will fall over and not get moving. (No reaction force will result if there's no friction)
     
  4. Sep 7, 2015 #3
    Thought so. Thanks for the clarifying.
     
  5. Sep 7, 2015 #4

    mfb

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    You can still move your feet.
    Walking in place is possible in principle, but in reality no surface is completely frictionless. On such a hypothetical surface, your "walking" direction and speed are completely independent of your actual motion (doesn't have to be in place).
     
  6. Sep 7, 2015 #5

    sophiecentaur

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    Ah well, now you are introducing practicalities. Fair enough but I was answering the question as it was put, which is a good way to start. You can walk (carefully) on ice but there's no way you can accelerate fast or change direction. If someone nudges you, you will go down.
     
  7. Sep 7, 2015 #6
    Really? You are right about the no surface being completely frictionless. Just one more thing; would you still be able to jump without friction at any height at all?
     
  8. Sep 7, 2015 #7

    mfb

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    Sure. The surface is still solid, vertical forces are possible (otherwise you would fall down through the surface).
    Would need some practice to avoid falling over.
     
  9. Sep 7, 2015 #8
    Alright. Just to make sure once more, in principle, it is possible to walk in place with no friction without falling over by slipping?
     
  10. Sep 7, 2015 #9

    mfb

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    In principle it is possible.
    You'll have to adapt the walking style a bit.
     
  11. Sep 7, 2015 #10
    Okay then. Thanks!
     
  12. Sep 7, 2015 #11

    sophiecentaur

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    With one proviso: the friction can only be very low and not zero. If it is zero then how can you change your lateral velocity by contact with the ground?
     
  13. Sep 7, 2015 #12

    mfb

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    The point is to not change the velocity.
     
  14. Sep 7, 2015 #13

    sophiecentaur

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    I read the OP as wanting to be able to move and not to have to stay in one spot. In which case you would want to change velocity (and control where you're going. Though the conversation has drifted about a bit.

    Staying in one spot when there is no friction AND staying upright, would be possible by whirling your arms about appropriately, I suppose. (Is this just an arm waving explanation? :wink: )
     
  15. Sep 8, 2015 #14

    A.T.

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    The OP specifically asks about "just walk in place".
     
  16. Sep 8, 2015 #15

    mfb

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    You can still accelerate even without friction, of course. Waving your arms in the right way is an option, blowing air in one direction works, ...
    This does not work in a frictionless vacuum, but then you have more urgent problems.
     
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