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I'm trying to understand precession for a gyroscope or top.

I do understand why precession occurs using the vectors for the weight force and torque and angular momentum. But what I don't understand is why precession only occurs at high angular speeds. Looking at the different vectors, there should still be a resulting change in the top's angular momentum.

I've tried to find an answer in my favorite physics textbook, but it only says that at lower angular speeds, the situation becomes much more complex. Which is not very helpful.

Can anyone explain the basic idea why precession only occurs at high angular velocities. I don't need this for an exam or anything, so I don't require a detailed mathematical explanation. I just want to get the basic idea.

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In general, a spinning top will exhibit three types of motion. First, it will rotate about its axis. Secondly, if a constant force is applied, this axis may precess around the direction a of the force. Finally, there is a process called nutation in which the angle between the axis of rotation and the force oscillates, creating a 'wobbling' motion.

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When the speed of rotation $\omega$ increases, the amplitude of the nutation decreases as $1/\omega^2$, which means that for 'fast enough' tops, the nutation may be neglected and you can simply deal with the precession.

If you want to see the mathematical details, Goldstein's Classical Mechanics deals quite extensively with this problem in section 5.7. For a more intuitive physical understanding, try Feynman's Lecture I.20.

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  • $\begingroup$ This PDF article has a very nice treatment of the nutation problem, following on the discussion in The Feynman Lectures. I think you could add that in the limit of low angular speed the nutation is large enough that the top rapidly crashes into the ground and you have very little time to observe the very small precession. $\endgroup$ – dmckee Feb 2 '14 at 17:54
  • $\begingroup$ That looks like a nice paper, and it includes a nice summary of what is and is not in the Feynman lecture. To help prevent link rot: doi and arxiv links. $\endgroup$ – Emilio Pisanty Feb 2 '14 at 18:16

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