Tuesday, 26 April 2016

newtonian mechanics - Lifting frictional force and relative values for kinetic vs static friction


My physics textbook says that friction mainly arises due to intermolecular attraction between atoms of the objects in contact and clashes between peaks are only significant for rough surfaces. I was wondering, if friction arises due to intermolecular attraction, why doesn't it oppose lifting a body as well(considering that the atoms are attracted to each other). Why doesn't it oppose rolling? (even when there is no slippage, if atoms of the contact patch are attracted to the atoms in the ground, there should be a force opposing movement)



Another related question: Is there an intuitive reason why(for most pairs of surfaces) kinetic friction is lower than static friction?




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