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Forces of the "Switch Pitch"

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  1. Oct 31, 2014 #1
    Hello,

    I've come across this toy called a "Switch Pitch" designed by Chuck Hoberman. It's a ball that when tossed into the air (with some amount of rotation), inverts and changes colour. Made of plastic, it's connected with numerous sockets and plates. It's quite hard to describe with words, so I'll include some links.

    http://i.stack.imgur.com/WWzUo.png

    Here's a picture of the ball in first position, then midair, then in its second position.

    A video of the ball being thrown:


    I'd really like to know about the forces that cause the ball to change colour, very curious about this.

    Thank you!
     
  2. jcsd
  3. Oct 31, 2014 #2

    Danger

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    Well, don't that beat all? I've never heard of such a thing. Even the slow-motion action is too fast for my admittedly poor vision, but I figure that it probably works on some variation of the Rubik's Magic puzzle mechanics, with something like fishline running through grooves in the plastic to act as universal hinges. There must be some kind of accelerometer (pendulum or such-like) to trigger the change, because I don't see him pushing any buttons or undoing latches. Hmmmm.....
    If they're not too expensive, I'd recommend buying one and taking it apart to see what makes it tick.
     
  4. Nov 1, 2014 #3

    A.T.

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    Here the manual switching:



    It don't have one, but judging by the videos there is slight tension that opposes the opening of the ball. If you provide enough spin, the tension is not sufficient to provide the needed centripetal forces, so the ball opens and switches. During the switch the aerodynamic drag increases so the spin slows down and the tension is now sufficient to close the ball again.

    Why doesn't that ball just go back and close into the original state? I guess it's the rational inertia of the individual parts. During the opening the individual parts gain some relative local rotations.
     
    Last edited: Nov 1, 2014
  5. Nov 1, 2014 #4

    Danger

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    Oh, who are we trying to kid...? It's witchcraft!

    Thanks for the new video, A.T. It's a bit clearer, but I still can't see what physical confinement method is actually holding the pieces together while still allowing such flexibility.
    Now, on top of that question, I'm going to be going nuts for hours chasing down all of the other weirdo puzzles that are subsidiary links to yours. (That one dude is holding between his hands what appears to be a small solar system on LSD. I'm not even going to look at that until tomorrow.)
     
  6. Nov 1, 2014 #5

    anorlunda

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    Does the device or it's literature cite a patent number?
     
  7. Nov 1, 2014 #6

    Hi A.T.: I got a message saying you invited me to look at this. I don't know who you are? Last week I visited two physics departments and I swear I saw about 5 of these on various office shelves. I have held one but not looked closely at the (clever) mechanism. But clearly it is bi-stable, like a light switch. Whatever the details, it is really cute. But I don't see a basic mystery.
     
  8. Nov 1, 2014 #7

    A.T.

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    I was wondering if it needs aerodynamic drag to close again, or if it would close completely in vacuum free fall too. If it actually would close completely again in vacuum, it would need to have the same angular velocity as initially (because of angular momentum conservation). But that is not possible because of internal energy dissipation. Unless the switch somehow changes the moment of inertia around the spin axis.
     
    Last edited: Nov 1, 2014
  9. Nov 1, 2014 #8
    The light switch analogy works for me here. It is like throwing a heavy light switch. When it collides at the other side, and doesn't bounce, it doesn't come back. The initial throw has some energy and some angular momentum. As you note, the angular momentum can't get lost without air friction. But the energy can. The energy is, in part in radial motion (and spring tensions) and that part gets lost when the ball resets to its new color position.

    So, I don't think air friction is important. It might help, but I really think it is not key.
     
  10. Nov 1, 2014 #9
    Thanks everyone for all your replies! I do have the ball, and I can tell you that it does not change when it is dropped without any spin. I also tried rolling it down my stairs, and everytime it was it the air between stairs, it went into that midair stage, and once it hit a stair, it went back into one of its stable states. I also noticed that the stairs were much more consistent than throwing the ball with my hand. With the stairs, the ball changed colour everytime, whereas with your hand, it sometimes stays the same colour.
     
  11. Nov 1, 2014 #10

    Danger

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    So am I, but it's manageable with proper medication...


    The basic mystery to me is how the damned thing works, which I believe is the point of this thread.
    Can you rephrase your post #8 a bit? It think that there might be a bit of a language gap here, because I'm not quite sure what you mean. Some of the terms seem incompatible.

    I'm really tempted to buy one, just to put on the shelf. It will fit in perfectly with my preserved crocodile head and full series of "Lost" on DVD.
     
    Last edited: Nov 1, 2014
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