What shaped pebbles?

No two pebbles are exactly the same, but all of them seem to come to a single mathematical form - a circular object with a distribution of curves almost according to Gauss's law, scientists claim. dad.

Complete pebbles often have the same shape, even when they are small. (photo: bourgetbros) And once this shape has been shaped, it will never change (at least in the experiment). When a large pebble is eroded to become a tiny particle, it retains its classic look.

This persistent puzzle was discovered by material physicist Doug Durian from the University of Pennsylvania in Philadelphia, USA and his colleagues.

Aristotle had assumed that the circle of pebbles was produced by faster lateral erosion in the middle - an almost complete explanation for why sharp corners were cut. Even so, our knowledge so far has not been far more advanced than Aristotle's.

Durian and colleagues said the best way to identify circular objects is to consider the presence of curves. A sphere has the same curves everywhere. But the curve of a pebble changes from one corner to another.

Durian's group studied pebbles made of solid mud in Mont St-Michel bay, on the northern coast of France. Here, the tides create fierce flat flakes of solid mud in many months. When the erosion process accelerates, the pebbles "complete" from their sharp appearance to a circle.

The team took two-dimensional pictures of more than 60 pebbles in different erosion states, and calculated the distribution of curves around the perimeter of each pebble. This distribution is made up of a graph.

In such a graph, the curve distribution of a circle will appear as a straight stroke. But all the pebbles are displayed in the form of a wide bell, and the older the " pebble " reaches its shape as described by the Gauss curve .

In addition, although the exact shape of the old pebbles is different, they all exhibit the same distribution of curves once they have passed some erosive phase.

The team said the distribution of curves does not seem to depend on the original shape of the pebble, but only on the process itself. It is possible that the lightening process will produce a narrower bell curve, and a shape that closely resembles the perfect circle.

This raises the hypothesis that experts can judge the origin of a pebble (such as in a river bed, or in a slow flowing water of a glacier, or erode by the wind) based on the shape it.

T. An