297Chap8 - Laws of dry or Coulomb friction "The...

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Laws of dry or Coulomb friction "The physical cause of the resistance offered by friction to the motion of surfaces which slide on each other can be explained either by supposing an interlocking of the roughness of the surfaces, which cannot be sepa- rated unless theyyield or break or are lifted overthe tops of on another ,or by supposing the the molecules of the surfaces of the twoplanes in contact are so close together that theydev elop a cohesion which must be over- come to produce the motion; experiment alone can enable us to determine the reality of these different causes." --Coulomb, The ´orie des Machines Simples ,(1779)
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CE 297 2 Laws of dry or Coulomb friction (cont) No motion ForPsmall, the body is in equilibrium. N = V + W F = P V W N F P Impending motion If P is increased, there is no motion until P = F m . N = V + W F = F m = P V W N F m P
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CE 297 3 Laws of dry or Coulomb friction (cont) Motion For P > F m ,the body moves. N = W + V F = F k < F m The unbalanced force P - F k = ma causes the body to accelerate with accleration a . a = P - F k m V N P W ma = F k
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CE 297 4 Laws of dry or Coulomb friction (cont) Coefficients of friction Experimentally, F m = μ s N F k = k N where s =coefficient of static friction k =coefficient of kinetic friction Since F k < F m ,then k < s .
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This note was uploaded on 01/20/2012 for the course CE 297 taught by Professor Pujol during the Fall '08 term at Purdue University-West Lafayette.

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297Chap8 - Laws of dry or Coulomb friction &quot;The...

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