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Scientists head for the beach to find out.
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.
Read the story here.
Posted by Nicola Jones on July 14, 2006
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Comments
Is the distribution normal
or is it just that not enough care has been given
to investigating it properly?
Posted by: Herman Rubin | July 17, 2006 06:54 PM
Intrinsically fascinating though this main story may be, I fail to see how this helps in the greater part of our lives. It is also puzzling why U. Penn researchers had to import pebbles al the way from Fance in order to do their studies.
Posted by: Roshni Mitra | July 17, 2006 07:01 PM
There was a section of beach at the north end of the Scripps Institution of Oceanography where one could find perfectly round pebbles of granite. So there must be more to the story. Under what conditions does the standard deviation of the Gaussian distribution approach zero?
Posted by: Robert Stewart | July 17, 2006 09:13 PM
In a quantavolution (large-scale, intense, sudden event) trillions of pebbles will be formed. This article is timely and significant. It suggests furthe research into 1)systematic measures of disorder applied to potentiated pebble-rock of typical compositions; 2) examination of Arabian barad and other great fields of angular stones that "should" long ago have become rounded pebbles; examination of samples of widely separated pebble deposits to produce a scale of pebbles of 'identical' composition correlated to scores on the Gaussian shapes.
Posted by: Alfred de Grazia | July 18, 2006 08:25 AM
Some of the questions raised are discussed in one of the authors presentation on the web. The site has also a little more material on pebbles.
http://ludfc39.u-strasbg.fr/talks/pebbles/pebbles.htm
Posted by: Carlos Marques | July 20, 2006 12:49 PM
The curvature distribution from the samples analyzed is certainly not a symmetric distribution. Note that there is an intrinsic asymmetry for purely convex polygons: the curvature has always the same sign. Most natural or lab made pebbles are predominantly convex.
This work shows that a given erosion process, in the laboratory, gives after a certain time a well defined distribution of curvatures, independent of initial shape and age. It is thus worth to take up the challenge of theoretically predicting the shape and the width of the distribution. Results from first attempts at this with computer simulations can also be found on the author's wesite.
Posted by: Carlos Marques | July 21, 2006 06:43 AM
Most attempts to describe the shape of a pebble have involved measuring the "aspect ratios" -- that is, the ratio of the longest to the shortest axis -- of pebbles. However, such methods cannot distinguish one shape from another and do not give geologists any idea about the erosion processes that led to the creation of the pebble. Geologists are interested in such processes because it would let them work out if, say, a layer of rock containing that pebble was formed from a lake, a river, an ocean shore or a desert.
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Gerard Kennedy
http://pointniche.org
Posted by: Gerard Kennedy | December 12, 2006 12:23 PM