A seaside conundrum has been solved: what shape is a pebble?
The answer, of course, is 'pebble-shaped'; but now, thanks to research by a team in France and the United States, it's possible to define what that means.
Technically speaking, says material physicist Doug Durian of the University of Pennsylvania in Philadelphia and his colleagues, a pebble is a rounded body with a near-gaussian distribution of curvatures. While no two pebbles are exactly alike, all seem to end up with a mathematical formula.
And once this shape is attained, it never changes (in lab experiments, at least). As a large pebble is ground down to a tiny grain, it retains this classic pebble shape.
Aristotle proposed that the rounded shapes of pebbles arise because of faster erosion of parts furthest from the centre, which neatly explains why sharp corners get worn away. But although various proposals have been made for how to define a pebble's shape, including simply measuring its width, breadth and height, our understanding has not advanced much since Aristotle's time.
3 comments:
jeez, dont they have anything else they could waste their time on?..like that tree falling in the forest thing...?
And this is what my tax dollars are funding?
Their next experiment is to work out how many gallons of water there is in the Pacific using a small plastic cup and measuring jug, they estimate this will take them about 439 million years and get them an honorary diploma ....
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