The Curious Behavior of Spinning Tops

  • Context: High School 
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Discussion Overview

The discussion revolves around the behavior of spinning tops, particularly focusing on the phenomenon where the direction of rotation appears to reverse as the top slows down. Participants explore the forces at play, such as gravity and friction, and the concept of precession in relation to the motion of the top.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant observes that spinning tops lose speed and seem to reverse direction just before stopping, questioning the forces involved in this behavior.
  • Another participant explains that the top experiences torque from gravity and friction, leading to precession, suggesting that the apparent direction change may be due to increased precession rather than an actual reversal of rotation.
  • A later reply clarifies that the top does not reverse its rotation but instead wobbles in the opposite direction after stopping, raising further questions about the cause of this wobbling motion.
  • Another participant expresses confusion about the relationship between the direction of the spinning motion and the direction of the rotational axis, questioning why the axis seems to reverse after the top stops.
  • A participant references the right-hand rule in relation to the discussion, indicating a potential connection to the observed phenomena.

Areas of Agreement / Disagreement

Participants express varying interpretations of the behavior of spinning tops, with some agreeing on the observations of precession and wobbling, while others raise further questions and uncertainties about the underlying mechanics. The discussion remains unresolved with multiple competing views.

Contextual Notes

Participants mention forces such as gravity and friction, but the discussion does not fully explore the assumptions or definitions related to these forces or the mechanics of precession. There are unresolved questions regarding the direction of motion and the relationship between rotation and wobbling.

LuGoBi
Wel, this is just crazy.

I've noticed something weird about spinning tops. Most of them start loosing speed, then, just before they stop, the direction of rotation is reversed! Why?! What is the force that makes them stop for a instant and then reverse the rotation?

If you have no idea what I'm talking about, take a look at this video: [Apparently, I can't post URLs to other sites yet, so just go to YouTube and search for a video named "Japanese Koma"]
 
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The top spins about it's own axis, but there are forces acting on the top (gravity, friction) that apply a torque to the top. This causes the top to precess, so in addition to the spinning about it's rotational axis, the rotational axis itself turns.

So I think if you could observe the transition in slow motion, you'll find that the top doesn't change directions, but merely that it's precession becomes more pronounced.

Only a guess though.
 
Uptade: Just noticed something. The direction of rotation is not reversed. The thing is, after the spinning top stops rotating, it "wobbles" a little bit, and that wobbling IS in the opposite direction of the rotation, but if you look at it carefully, the top isn't rotating anymore, it's just wobbling. Now the question is: why does it wobble, and why does it do it in the opposite direction of the previous rotating motion?
 
Ibrits, I hadn't read your message before posting my second one. Seems like our observations agree. Very interesting. Thanks for the answer.
 
Allright, this isn't settled yet.

How come, WHILE the top is spinning the rotational axis is also spinning in the same direction of the motion? Then when the top stops rotating the rotational axis reverses it's direction of motion. Why does that happen? And what defines the direction of precession?
 

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