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Toy top in space

  1. Apr 15, 2008 #1
    Sorry if this is the wrong forum. I looked in the FAQ, but since this isn't a homework question and doesn't fit the syntax of asking it, I thought here was the best place.

    If I started spinning a toy top in dead space, would the top ever stop spinning?

    My first guess is 'yes, it will stop,' because the motion of the top is accelerative, and in order to keep spinning must continue to accelerate in more than one direction. However, I'm not sure if I remember enough of GR to figure out where the initial energy of spinning the top ends up (or if this question is a sort of fallacy in this situation), and I did a google search before coming here where there was supposedly an experiment carried out like this to prove that the top does keep spinning.

    Any help here?
  2. jcsd
  3. Apr 15, 2008 #2
    Angular momentum is conserved, so it is only interactions with other material or releasing radiation that could make the top stop spinning. (ie. if it is a closed system, the system can't loose angular momentum)

    Since you asked for an experimental example, the first thing that came to mind is the Einstein Probe B experiment which had some of the most precise gyroscopes ever built. These are basically spinning tops. The rate of the spinning was constant enough to allow measurement of some subtle features of the curvature of spacetime around the earth (despite even some slight interactions due to our requirement that we need it to be a non-closed system so we can measure it, and uncontrollable interactions due just to other material enclosing the device).

    Since you mentioned GR, you may also be thinking about gravitational radiation. While it would take an incredibly long time for this to affect just a toy top, if the top has a non-zero quadrapole or higher order mass distribution, it will radiate gravitational waves and very very slowly slow down.
  4. Apr 15, 2008 #3
    So, even though the top is accelerating, so long as the acceleration is purely in terms of velocity, it does not require continued energy to stop accelerating?
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