How Does a Slow Spinning Gyroscope Behave Compared to a Fast One?

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Discussion Overview

The discussion revolves around the behavior of slow spinning gyroscopes compared to fast spinning ones, focusing on concepts such as angular momentum, precession, and the effects of mass and torque. Participants explore theoretical implications and practical observations related to gyroscopic motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question whether a slow spinning gyroscope behaves like a fast spinning one, suggesting that the answer depends on specific conditions.
  • It is proposed that if the mass of the gyroscope is large enough to equal the angular momentum of a fast spinning gyroscope, its precession could be similar, provided the applied force is the same.
  • One participant notes that the precession rate remains constant if the moment of inertia increases while angular momentum and torque are fixed, but this holds only under certain conditions.
  • Concerns are raised about the validity of the precession speed equation at low rotation rates, indicating it may not apply accurately in those scenarios.
  • There is a question about whether a gyroscope suspended by one end under gravity will fall or precess, with differing opinions on the outcome.
  • A participant revises an earlier claim, asserting that the equation for precession is exact rather than an approximation, and discusses the implications of angular momentum alignment during precession.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of slow versus fast spinning gyroscopes, particularly regarding the conditions under which precession occurs and the applicability of precession equations. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Limitations include assumptions about the conditions under which precession equations apply and the definitions of angular momentum and torque in relation to gyroscopic motion.

basheer uddin
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how does a slow spinning gyroscope behave?
does it behave as a normal fast spinning gyroscope would?
if the mass of the gyro is large so that the angular momentum equals a fast spinning gyro does its precession equal a fast moving one?
can anybody explain?please.
 
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does it behave as a normal fast spinning gyroscope would?
Depends on what you are doing.

if the mass of the gyro is large so that the angular momentum equals a fast spinning gyro does its precession equal a fast moving one?
If the force is the same: yes. This can be seen from the equation for the precession speed.
 
mfb said:
Depends on what you are doing.

If the force is the same: yes. This can be seen from the equation for the precession speed.

This holds so long as the precession rate is small compared to the rotation rate. If the moment of inertia of the rotating object is made larger and larger while angular momentum and applied torque are held fixed, the precession rate remains constant, but the rotation rate decreases.

The equation for precession speed is an approximation. If rotation rate is low compared to the computed precession rate, it fails to hold, even approximately.
 
Last edited:
so does it fall down if suspended by one end of the axis under the action of gravity or does it precess to one side?
 
basheer uddin said:
so does it fall down if suspended by one end of the axis under the action of gravity or does it precess to one side?

It will simply fall down.

On reflection overnight, I realized that what I wrote in post 3 is not correct. MFB is right The equation for precession -- as a rate of change in angular momentum under a torque at right angles to that angular momentum is exact. It is not an approximation.

A problem is the description of the movement of the gyroscope as a rotation about a fixed axis of symmetry where that axis is itself moving according to a precession. If the gyroscope is precessing rapidly enough to matter then its angular momentum vector will not align perfectly with the axis of symmetry. It will have a component corresponding to the "precession". In other words, when it precesses, the angular momentum of your gyroscope only approximately lines up with the axis that goes through its bearings.

A torque that you apply perpendicular to the axle of a precessing gyroscope will not be at right angles to its angular momentum.
 

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