Question |
| Asked by: |
Victor Geere |
| Subject: |
Newton and precession |
| Question: |
A lot seems to be said about Newton here, and it is often attempted to "prove him wrong". A statement that I feel obliged to make is that precession is neither an action nor a reaction in terms of Newton's laws. It is motion.
1. An object at rest tends to stay at rest and an object in motion tends to stay in motion
with the same speed and in the same direction unless acted upon by an unbalanced force.
2. The acceleration of an object as produced by a net force is
directly proportional to the magnitude of the net force,
in the same direction as the net force,
and inversely proportional to the mass of the object.
3. "For every action, there is an equal and opposite reaction."
In the second law, pay attention to the word "net". The spin of the gyroscope, and for that matter, ALL forces have to be taken into account.
As for the 90 degree precession motion, I suspect that, in the absence of aditional friction, the external force will cause the gyroscope to turn an aditional 90 degrees in the same direction as the spin when it precesses through a 90 degree angle. Needless to say, a total of 180 degrees. For the axis of the gyroscope to turn at a 90 degree angle the forces on either side of the gyroscope act in opposite directions and eventually align with the direction of spin of the gyroscope after it turned through the 90 degrees. |
| Date: |
26 April 2005
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Answers (Ordered by Date)
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| Answer: |
Eric James ----- - 05/05/2005 05:36:22
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| | Victor,
You seem to have it right through the laws of motion part, but that last paragraph isn't very clear. Can you elaborate?
Eric
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| Answer: |
Victor Geere - 05/05/2005 12:54:18
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| | From the moment the spin of the gyroscope starts to align with the external force, the spin of the gyroscope benefits from this external force, up to the point that the axis has turned 90 degrees after which all the external force is converted into spin. Also count the number of 90 degree turns ilustrated in the diagram. There are two.
Precession
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| Answer: |
Victor Geere - 05/05/2005 12:57:13
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| | Click on "Precession" above for the diagram.
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| Answer: |
Eric James ----- - 07/05/2005 06:19:44
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| | Victor,
Sorry, I'm still not understanding what you're driving at.
Do you mean that forcing the gyro to precess will add angular momentum to the gyro itself?
Eric
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| Answer: |
Victor Geere - 09/05/2005 08:44:32
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| | referring to the last paragraph of my post:
I don't know, but that is the hypothesis. Maybe only if the flywheel precesses around it's own centre of mass? It does seem like the vectors that cause precession benefit the spin.
Luis Gonzales made me think in this direction when he said that precession causes the external force and the direction of spin to align. It would make sense that the vectors would act in unison as soon as their direction starts to align. That is the hypothetical question, and a hypothetical answer is not going to solve it, so I'll stop typing now.
Victor
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| Answer: |
Eric James ----- - 10/05/2005 08:10:30
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| | Victor,
Okay, I think I might understand what you are thinking about.
As far as I could discern from you diagram, you show it wobbling up (I pressume) like from a table top? Is that correct? You know, self-stabilization? Like spinning a top?
If this is the case then I tend to agree with you. The wobble's energy is absorbed into the spin of the whole gyro assembly.
What usually happens though, is the the gyro's momentum actually transfers momentum into the frame and the whole thing spins together as a unit. But, I suppose that technically, the wobble's momentum is included in there.
Eric
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Victor Geere - 11/05/2005 09:21:06
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| | No, I wasn't referring to wobble. The gyro is on it's side and it is forced to turn on a horisontal plane but responds on a vertical plane due to precession.
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Eric James ----- - 12/05/2005 06:44:01
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| | Victor,
Oh! Now I see!
Wow, that's an interesting question.
I can see that it causes a rotation of the axis, but I don't think it will add this rotation to the gyro itself.
Arguably, since it is harmonious to the rotation, bearing load is decreased, except that you wouldn't have bearing load if you wern't precessing the gyro to begin with.
Kind of a Catch-22 situation.
So, I'd have to say no, unless experiment proved otherwise (not always wise to trust one's off-the-cuff judgement).
Eric
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