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Falling Tic-Tac dynamics.

  1. Feb 18, 2012 #1
    Ok, just a few minutes back, a tic-tac slipped from my hand and fell to the ground.

    The second bounce was to a lower height than the first (which is expected because e*<1) but then as it took the third bounce, it rose to a height higher than the one reached by it than in the second bounce.

    I had observed this phenomenon before in pebbles, but today I sat down and started thinking about it, I came up with the following result :

    I noticed (after dropping the tic-tac about a hundred times) that the height of a bounce is higher than the one preceding it only in one particular case : when the tic-tac hits one end on the floor first and then hits the floor a second time before bouncing back.

    To make sense of this, I followed energy conservation.
    The tic-tac originally has a potential energy of mgh and when it bounces back to a new height, it has no transnational kinetic energy, some potential energy and most importantly: Rotational kinetic energy.
    Now to make the tic-tac reach a max height, the rotational kinetic energy would have to be minimum.
    So what actually happens is that when a tic-tac hits the floor a second time in the same cycle, it gets a torque in the opposite direction to what it got in the first hit in the same cycle, hence reducing the rotational and by conservation of energy, making it reach to a higher height.

    That's what I came up with, is it even remotely correct to what is actually going on? Any other thoughts?

    *e = coefficient of restitution
  2. jcsd
  3. Feb 18, 2012 #2


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    Hi AlchemistK! :smile:
    Wow, that's amazing … I didn't know you could do that with tic-tacs! :biggrin:

    Yes, that seems a correct analysis.

    I wonder whether there's a similar manouevre in gymnastics?

    I think you should do a few more experiments, and then publish!

    eg, what's the coefficient of restitution for a tic-tac? :wink:
  4. Feb 18, 2012 #3
    I have a counter reasoning too though, since the tic-tac hits for a second time, it looses more energy as heat and sound.

    How do I do that? With all the various uncontrollable variables like friction, angle of drop, and other things, it seems impossible.

    And also, I noticed that the phenomenon occurs more when the tic-tac is dropped at a certain angle, further supporting that the reasoning is correct because the tic tac would only hit twice if dropped at a certain angle.
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