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Q & A: internal friction

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Most recent answer: 09/07/2012
is there any friction between internal molecules of the spring(during expanding&compressing) apart from air,body to surface contact friction? also tell how the molecules behsve when the spring oscillating?
- sathishkumar (age 19)
Yes, as any springy material flexes there is internal friction. That's true whether the material is made out of molecules, like typical plastics, out of crystals of atoms, like most metal springs, or out of glassy arrangements of atoms or molecules, like some other materials. It even applies to springs made out of gases, like ones based on sealed pistons of air. We can't give a detailed microscopic description that would apply to all these sorts of materials.

Just to pick one sort of example, in a typical metal spring there are many defects in the crystal. Say that you have a very simple defect- an extra atom sitting somewhere in the crystal. As the spring flexes, there's a little strain which makes it so that if the extra atom hops over sideways it can have a little lower energy. If it does, the extra energy gets released as sound waves (phonons), heating things up a little. That's internal friction, turning some mechanical energy into heat.

Mike W.

(published on 09/07/2012)

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