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sir i have studied through various websites. there i found two theories-

  1. friction is due to inter molecular bonds which forms when two surfaces kept together.

    now if it true then why do we not feel extra resistance when lifting objects.

    this theory says that heat is generated due to making of these bonds.

  2. friction is due to normal forces exerted by the lower surface on the upper surface in the irregularities.

    i read according to this theory heat is generated due to slight deformation of molecules.

please guide me which one of these is correct and why, and why the other theory is not correct?

Qmechanic
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Lokesh
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1 Answers1

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On a microscopic level, almost no surfaces are perfectly smooth, they have peaks and valleys. For static friction the peaks of one surface are meshed into the valleys of the other. A normal force acts to lock them into this position. (The larger the normal force, the stronger the lock.) In kinetic friction, the peaks of one surface are colliding with those on the other (and generating heat in the process). A normal force makes these collisions more severe.

R.W. Bird
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