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Talk:Rattleback

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This is an old revision of this page, as edited by Melchoir (talk | contribs) at 07:07, 1 March 2012 (→Original poem: new section). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Size

Not sure how relevant the size is. Of course the ratio gravity force/friction is important, so the range of sizes which exhibit spin reversion will depend on the material but especially of the surface roughness (which depends more on surface treatment than on material) of both the rattleback and the support on which it is spun. --Josce 14:35, 14 December 2006 (UTC)[reply]

Could be fun to try one the size of a small boat as a see-saw, with an eccentric seat at each end - see if you could influence (or even pump) the oscillations by moving your body ? Maybe if you could feel the forces acting on yourself then it would be easier to understand ? Possible fairground ride ? I wonder if David Elsewhere has considered using rattleback dynamics in his dancing ?

--195.137.93.171 (talk) 04:08, 11 February 2008 (UTC)[reply]

References

Removed

  • Elliott, W.A. The inside story of the whirlygig! W.A. Elliott Co., Toronto.
  • Elliott, W.A. The Tate's compass. W.A. Elliott Co., Toronto. 1982.
  • Freeman, Ira B. "What is Trevelyan's rocker?" The Physics Teacher, 12:382. American Association of Physics Teachers. College Park, Md. 1974.

Tate's Compass is a compass which has no marking or wrong marking to differentiate North and South ! Trevelyan's Rocker is a thermal oscillator ! Whirligig seems to be suspended and wind-driven

I guess they are referred-to in some papers about Rattlebacks, but weren't checked before adding ? Can anyone see others ? --195.137.93.171 (talk) 01:46, 11 February 2008 (UTC)[reply]


Multiple reversals of spin ?

There are a couple of reports of the direction of rotation (yaw) changing twice.

'I can spin it with the weight in one direction and it turns back twice - it doesn't like spinning in either direction.
However if I spin it in the other direction, it wobbles about a different axis, comes back, wobbles faster, and comes back again'
'If there is less friction, it may indeed happen that it once again changes rolling direction.'

(Computer simulation - I suspect the animation is just looped)

'In several of the celts that I have made the +yaw motion couples into a rolling motion and the rolling motion couples into -yaw motion.
The problem is that while the coupling between -yaw and pitch and between pitch and +yaw are strong, the coupling between +yaw and roll and between roll and -yaw are very weak.'

Even this article says:

'Glass rattlebacks, however, were reported to exhibit "unstable behavior" when spun in either direction, and incur up to four or five successive rotations during a single experiment.'

I presume 'rotations' here means 'changes of rotational direction (yaw) from clockwise to anti-clockwise or vice-versa' ? Anyone know who found this, and how ?

I added "Some exceptional rattlebacks will reverse when spun in either direction" at the top of the article. Have I done the <ref> links OK, to tie the fact to the source ?

--195.137.93.171 (talk) 02:44, 11 February 2008 (UTC)[reply]

Yes, there are rattlebacks that work in both directions. The axis for the up and down oscillation is different in each case. What has not been addressed here is the source of the reversal torque. It cannot be gravity since gravity is vertically downwards. It cannot be friction since friction doesn't store energy and recoil it. David Tombe (talk) 17:02, 17 November 2008 (UTC)[reply]
LOL. It can be friction since in a rattleback the friction doesn't act quite along the line of rotation, and this exchanges angular momentum with the plane it's sitting on.- (User) Wolfkeeper (Talk) 17:49, 17 November 2008 (UTC)[reply]

Wolkeeper, friction could slow something down. But I've never known of friction to go on a counter-offensive. David Tombe (talk) 20:12, 17 November 2008 (UTC)[reply]

Then you weren't paying attention. Throw a lot of oddly shaped things along the ground and watch their crazy gyrations, particularly towards the end.- (User) Wolfkeeper (Talk) 20:53, 17 November 2008 (UTC)[reply]

That doesn't explain how friction could possibly cause the reversal torque in the rattleback. Interestingly, static friction is absolutely necessary for the full operation of the rattleback, but sliding friction damps the effect. If there is no static friction, then the rocking stage can't happen. If there is no static friction, the rattleback slides and the rotation gets damped out. Try it on ice and see. David Tombe (talk) 22:07, 17 November 2008 (UTC)[reply]

There's no mystery here. It exchanges angular momentum with the base it's resting on. Sliding friction can do this as well, but if there's too much slip then it will stop before turning around. Static friction conserves energy.- (User) Wolfkeeper (Talk) 22:19, 17 November 2008 (UTC)[reply]

Wolfkeeper, I'm afraid we're going to have to agree to differ on this issue. David Tombe (talk) 22:47, 17 November 2008 (UTC)[reply]

Original poem

I'm removing this poem from the article, because I couldn't find its source:

Behold the mysterious celt,
with a property that amuses.
One way it will spin,
the other way it refuses.

It was added with this edit. Melchoir (talk) 07:07, 1 March 2012 (UTC)[reply]

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