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Pause for thought.

There is a curious device known as a 'Rattleback', (also called 'celt', 'rattlerock', 'spin bar', 'wobblestone' and more) which I sometimes use to rouse students interests in technical matters. It's a simple piece of plastic, about 8cm long and 1cm wide, flat on one side and curved on the other. If you place it curved side down on a smooth flat surface, you can spin it anti-clockwise quite readily. However, if you spin it clockwise, it soon stops, performs a rocking motion, and begins to spin the other way. You can also get opposite hand ones which perform in the other direction.

The secret is that the curvature is not aligned with the longitudinal axis. The line of minimum curvature is skewed. The theory is complex, as an internet search will soon show. The originals were first found in archaeological digs of Celtic and Egyptian sites over a century ago. Watching their behaviour, I can't help but think there must be a use for them, but I haven't thought of it - yet.

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Title Annotation:LETTERS
Author:Ledsome, Colin
Publication:Engineering Designer
Article Type:Brief article
Geographic Code:4EUUK
Date:Jul 1, 2011
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