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It's funny. Laugh. Science

Solution to the 'Spinning Egg' Problem 25

Posted by timothy from the hard-boiled-science dept.
SuperAbe writes: "According to an article in this week's issue of the journal Nature, mathematicians Keith Moffatt of the University of Cambridge and Yutaka Shimomura of Keio University, Yokohama, Japan have discovered why hard-boiled eggs spun on their side stand on end spontaneously: friction."
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Solution to the 'Spinning Egg' Problem More

Solution to the 'Spinning Egg' Problem

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  • Now if only they could solve the mystery [endeavorz.net] of where the easter bunny gets his eggs.
    My favorite quote from the article:

    Nickel has analysed the physics of the 'tippe-top', a mushroom-shaped toy that flips from spinning on its round end to its stalk
    It's good to know that our greatest minds are working on these things.

    -Sou|cuttr

  • Raise your hands (Score:5, Funny)

    by nosferatu-man ( 13652 ) <spamdot@homonculus.net> on Friday March 29, 2002 @01:40PM (#3248502) Homepage
    ... everyone who *knew* that there was a "spinning egg" problem.

    Peace,
    (jfb)
    • I'd heard of it. I'd also heard this general solution proposed on my undergrad course, it's just noone could be bothered to mess around with all the damn vectors until now.
    • Well, I knew about the effect, but I didn't know anybody had a problem with it. Hey, if eggs want to rotate erected, that is their business!

  • Simple explanation for physics geeks (Score:4, Informative)

    by Viadd ( 173388 ) on Friday March 29, 2002 @03:33PM (#3249158)
    I didn't know there was any mystery about spinning eggs standing up. I haven't read the Nature paper, but here is a simple explanation (for those who have had second year physics).

    A spinning body has both angular momentum and rotational energy. For a given amount of rotational energy, it has the lowest angular momentum when its mass is closest to the spin axis, and the largest angular momentum when its mass is farthest from the spin axis. These correspond to the spin axis aligned with the length of the egg, and across the egg, respectively.

    When you start an egg spinning on its side on a tabletop, it is in its largest angular momentum state for that particular amount of rotational energy.

    Because the egg is not a perfectly symmetric ellipsoid, and because of reality, the point of contact with the table at any given time is not perfectly aligned with the spin axis. This causes a force which gives a torque that reduces the angular momentum. If the egg also slipped across the surface, it would lose energy due to dynamic friction, but the energy loss is minimal if the friction makes the contact point roll along.

    The egg now has reduced angular momentum but unchanged rotational energy, and to compensate it has to bring its mass closer to its axis, which it does by bringing its long axis closer to its spin axis, i.e. standing up. This also reduces the rotational energy of the egg by converting some of it into potential energy (the center of gravity of the egg is raised) which helps bring things into balance.

    The eventual result is an egg standing on end.

    • Sounds like a similar situation to the "mystery" of why coins spin faster the closer they get to stopping; it's not thet they're spiining faster, it's just that there's more edge touching the surface that it's spinning on, which makes more noise.
    • You obviously didn't read the article.

      "You have to have slipping between the egg and the surface," advises Moffatt. "If you tried this on a hard rubber table it wouldn't rise."

      While your explaination is partially correct, you missed the whole point of the article.

  • Friction is Fun (Score:3, Funny)

    by Veramocor ( 262800 ) on Friday March 29, 2002 @05:27PM (#3249799)
    F = uN
    • I'm sorry to say, but a friend (Carson William Werner) and I have already made this joke, so I think that you should at least cite my last name (Raynor) as well as his (Werner) before you steal another slab of our infinitesimal humor cake. Yes, that is correct (infinitesimal), we are very unfunny. Back on topic, I heard a report on NPR about this egg-spinning physics, but they blabbed over the entire scientific explanation. Oh well.
  • "I think it prefers to go up on the sharper end," Moffatt speculates.

    I think Freud could have a lot of fun analyzing this egg.

    Do you think it is attracted to the chicken that laid it?

  • You can stand them on end [straightdope.com], too.
  • There is nothing wrong with the research in the paper but why did Nature publish this? Seeing as it is so selective and only publishes papers of the greatest significance, this paper seems an odd choice for such a prestigious journal.

    If no other work had been done on this problem before then there would be no issue here but other papers have been written, and they are referenced in the Nature paper. Curiously, those other papers also make the point that friction is necessary to make the spinning object stand up. The only real difference here is that the egg is chosen rather than a tippy-top (which is more like half an egg with a stick on it).

    Overall, this paper seems to be an incremental contribution and a small one at that. (The general ideas as reported widely are well-known - for many years I have taught classes that the reason a tippy-top, spun football, etc. stand on end is because of friction+conservation of angular momentum, etc.)

    Or maybe Nature was just caught up in the Easter spirit...or maybe looking for good publicity... I wonder how long they had been sitting on the paper waiting for the Easter issue to come out...

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