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Distinguishing between Raw Egg and Hard-Boiled Egg

  1. Jan 25, 2015 #1
    1. The problem statement, all variables and given/known data
    Why does a hard-boiled egg spin faster than a raw egg?
    Why does a raw egg spin longer than a hard-boiled egg?

    Can this be explained using moment of inertia, angular velocity and conservation of angular momentum?

    2. Relevant equations
    Can this be explained using moment of inertia, angular velocity and conservation of angular momentum?

    Or can this be explained only on the basis of the liquid inside the raw egg which keeps on rotating and thus makes the raw egg rotate longer and as it opposes/slides against the inside of the shell, it slows down the egg?

    3. The attempt at a solution
     
  2. jcsd
  3. Jan 25, 2015 #2

    Simon Bridge

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    It is about the difference between the way gooey stuff responds vs how a rigid body responds - also about the mass distribution inside the egg, and the interaction between rigid and gooey stuff.
    You have to break down the process involved in each test ... how do the different parts of the egg respond to attempts to change the motion.

    It is also hard to spin a raw egg on it's point, and if you touch a hard-boiled egg that is spinning rapidly on it's side so it stops, but very quickly release it, it will resume spinning.

    Note: if you have never seen these effects, you should get some eggs and try it. Careful observation will (should) help with your answers.
     
  4. Jan 25, 2015 #3

    haruspex

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    Clearly that is not a general rule. It must assume something constant about the circumstances. Was there any more text to the question?
    For this one, it may be the same presumed constant circumstance, or maybe this is assuming the same initial spin rate. Either way, I do not believe the statement is true.
    What does happen is that if you stop the spinning egg and immediately let go again, the raw egg will resume turning.
    http://www.planet-science.com/categories/experiments/magic-tricks/2012/03/spinning-eggs.aspx
     
  5. Jan 25, 2015 #4

    Simon Bridge

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    Admittedly I havn't seen the second one either and I think it refers to the stop-release method.
     
  6. Jan 25, 2015 #5
    Didn't get that much. Could you please provide a more detailed explanation? If the moment of inertia of of the raw egg increases, how does it effect the velocity with which it rotates?
     
  7. Jan 25, 2015 #6

    Simon Bridge

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    Um, no, the idea is that you do the work.
    But it is not entirely about the moment of inertia of the whole egg - but about the different parts, where they are, and how they are connected together.
     
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