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Posted by David Williams on October 24, 2006, 10:20 am
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-> The scarp seems to be about 30 degrees or so, with considerable erosion.
-> This angle is typical of sand dunes and coal tips, even table salt if
-> you make a small pile on the kitchen counter-top.
-> The reason is that sine 30 degrees = 0.5, and so horizontal frictional
-> forces holding a rock in place is just balanced by vertical gravity
-> causing it to tumble.
That's just babble. Different materials have different coefficients of
friction. The shapes of the particles are important. If fluids are
present, they can have lubricating effects. Some solids, notably ice,
deform slowly under moderate forces. And so on...
It's true that piles of small particles tend to assume moderate slopes.
But there is nothing special about a slope of 30 degrees.
dow
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