High Quality Content by WIKIPEDIA articles! Precession is the name given to the process of one part rotating with respect to another due to fretting between the two. It is described as "precession, in which a round object rolling in a circular ring in one direction will itself turn in the opposite direction." "In machinery, fretting is the micro-motion of tightly fitting parts that superficially appear immobile with respect to each other." "For a pedal, a rotating load arises from downward pedaling force on a spindle rotating with its crank making the predominantly downward force effectively rotate about the pedal spindle. What may be less evident is that even tightly fitting parts have relative clearance due to their elasticity, metals not being rigid materials as is evident from steel springs. Under load, micro deformations, enough to cause motion, occur in such joints.

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