1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Hardest physics question/task. No naysayers please! Thanks

  1. Mar 30, 2013 #1
    Hardest physics question/task. No naysayers please! :) Thanks

    Here's The Challange:​

    I realize that this may be better suited to be posted on a magic/illusion type forum, but without implementing gimmicks and gadgets to perform this is more a task/question for physicists than illusionists.

    I am really grateful for any help I receive, and the title isn't representative of a pretentious attitude. I just can't stand it when people deem something impossible or dismiss a viable thought or idea as impossible without exerting any effort to solving it! :) (though I'm sure there will be people who will focus more on the "No naysayers" title rather than the question itself. )So thank you for any help.

    Okay, here is the challange/task that I am trying to overcome.

    It isn't very hard to understand how one would achieve this, but performing it is a different story. The forces at play are of course gravity, friction, other resistive forces, and a few others I'm sure I forgot.

    Imagine standing on one foot with the other leg off the ground as in the picture provided.


    Now imagine the foot that is on the floor sliding forward without placing the other foot down or holding on to something.

    There are two main groups that I would say it is achievable by, the gadget way and the non-gadget way. And by gadget I mean a device of any kind that allows you to do this(rollerblades).

    Without Gadgets

    I am wondering if it is possible to do without the aid of some kind of enhancement. This is why I am asking physicists! Such as a weight shift simultaneously of your suspended leg moving backwards as the foot on the floor slides forward.

    Anything you can think of that would allow you to do this? I am almost sure that with the proper leaning position (to give yourself something to pull against) and proper muscle strength it is possible. But I could be wrong. What do you think? Is there a way to do this without gadgets?

    With Gadgets

    I imagine a device within your shoe that vibrates, which would disrupt the force applied by friction, and allow you to more easily slide your feet on the floor. That is my best idea when it comes to this! How about you? Of course there's always WHEELS, but that is worse than cheating.

    I thought about magnets, but couldn't think of a way to apply them here. Anything from you guys?

    Okay, so as I said, it is a hard task to accomplish. But I think it is possible to not defy the laws of physics, but deceive the eye to thinking you have. Keep in mind that a JERK or jump forward is not sliding. There is a move in dancing called the (reverse) running man that is a lot like what I am talking about, but it implies both feet and a JERK movement to send the feet forward. Which is very wrong.

    Here's a good example of what I am NOT talking about:

    So what do you think? If you trained long enough, with sufficient strength in your quads and calves and a good leaning position(think smooth criminal lean by MJ), I think you could pull it off?

    All help with and without devices is welcomed! Thank you very much.
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Mar 30, 2013 #2
    I got an idea but is so simple that it might not sound interesting. In the end 'magic' (read illusions) are all boring when trick is revealed.

    If you set up environment in such a way that floor would look to be straight while in truth it wouldn't be, thus achieving it by optical illusion, perhaps by placing specially made chairs, tables and the rest of room equipment, which are bent and thus compensating for bent floor. Then you just get ice on the floor and sliding is made easier/possible.

    Another, silly sounding, idea is, to use strong, thin thus transparent wire to pull...

    Personally I'd like magnets best... There are very strong magnets which could be used. Easiest in theaters, where you can have people and equipment under floor. Shoe made by magnet and under the floor another magnet which is moved...

    Yet another idea is to have all floor to be movable, whole of it like one assembly line...

    Probably not what you expected lol
    Last edited: Mar 30, 2013
  4. Mar 30, 2013 #3
    Hey Boy@n,

    Good ideas indeed. I hadn't thought of the sloped floor illusion! I you're going that route, as in for a video or something, another thing that I thought of is a plexiglass wall with plexiglass pegs attached. Have the camera centered so that it could not detect the reflections of the glass or pegs and simply rest your weight on the pegs and pull yourself forward with the suspended leg.

    This is cool for a video or gimmick, but to be able to do it in front of a crowd with no assistance is the ultimate dream for me! Thanks for the input though.
  5. Mar 30, 2013 #4
    I like the sloped floor idea. Have you seen this actually done, or have you just heard of it or thought about the possibility?
  6. Mar 30, 2013 #5
    Glad you both liked that kinda gadget free idea - and yes, just thought of it after reading this post...

    What about using nano robots as 'gadget' for this job? Costly but not sure if possible... Would they be powerful enough to move such weight? ... well, at least not much friction if set properly...
    Last edited: Mar 30, 2013
  7. Mar 30, 2013 #6


    Staff: Mentor

    Just push the lifted leg back quickly. This accelerates your COM back. If the acceleration is high enough and the friction low enough then the foot will slide forward. Buckling the standing leg can reduce the normal force and friction.

    Or you can reduce the friction to 0 by hopping.
    Last edited: Mar 30, 2013
  8. Mar 30, 2013 #7


    User Avatar
    Gold Member

    Have her pull the shoe off the raised foot and throw it backwards over her shoulder at 0.9c.
    On a frictionless surface, she will be one with the opposite wall in some finite amount of time.

  9. Mar 30, 2013 #8
    I think that constitutes a jerking motion though, which the OP explains is ruled out.
  10. Mar 30, 2013 #9
    some contraption in the idealized shoe that turns some downward force into a forward one.

    Like those funny "see-saw" things on train tracks. A "handcar" I guess they're called.

    transferring weight from ball of foot to heel is a good "see-saw" action.
  11. Apr 2, 2013 #10
    Friction between the shoe and the floor could be minimized by making the shoe out of ice. Make yourself a mold of the shoe, fill it with water, add coloring so that it will match the other shoe, freeze it, and put it on.

    The downside to this method is that it increases the likelihood of getting cold feet right before your performance.
  12. Apr 3, 2013 #11


    User Avatar
    Science Advisor

    You can buy shoes with buildin (hidden) rollers. You can make them one way rollers with a ratchet hub. Then you can push back gently with the standing leg.
  13. Apr 3, 2013 #12
    Go buy a pair of frictionless shoes.
    Problem solved .
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook