I couldn't find it on YouTube either, and I couldn't persuade my son to do it, so I became the actor http://www.youtube.com/watch?v=Rzt_byhgujg On Sun, May 22, 2011 at 8:59 AM, Fred lunnon <fred.lunnon@gmail.com> wrote:
One standard demonstration of this phenomenon goes by the name "the soup-plate trick" --- moving only one arm, without moving the feet or changing the grip on the dish, the (full) dish may be returned to its initial position after rotation through any even number of full turns --- but NOT odd.
A sadistic demonstrator will invite his victim to perform the trick with a full beer mug instead: the natural approach of seizing the handle of the mug may lead to grisly contortions followed by beer on floor, performer, and audience.
I can't find a demo on you-tube. How about putting one up, somebody? WFL
WFL
On 5/22/11, Andy Latto <andy.latto@pobox.com> wrote:
On Sun, May 22, 2011 at 9:57 AM, James Propp <jpropp@cs.uml.edu> wrote:
Has anyone built a macroscopic object that has spinorial behavior but is not tethered to a frame by strings or ropes? (For an example of what I don't mean, see Ethan Bolker's article "The Spinor Spanner".)
Your body is such an object!
Stand facing a wall, arms straight out in front of you, at a distance where you palms just touch the wall. Now rotate one arm in as large circle as possible in a plane perpendicular to the wall; that is, keeping is straight, bring it down, then away from the wall, then up, then towards the wall again. observe that your palm no longer touches the wall. Now repeat the process with a second circle, and observe that your hand now touches the wall.
It's not a perfect example, because you don't have the freedom of movement to rotate your arm through 360 degrees in any but that one direction. And it's tethered to the rest of your body (though not by string or ropes, unless you count tendons and ligaments). But it's still cool.
Andy andy.latto@pobox.com
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