轉動摩擦力 的計算問題? (維基百科內容..

Rolling friction occurs because a sphere, cylinder, a wheel or any spherical object and the surface upon which it rolls are deformed slightly during contact. The magnitude of the rolling friction between dry surfaces is influenced by the coefficient of friction between the surfaces in contact, the normal reaction force, the radius of curvature of the rolling object, and its deformability.

The rolling friction F is given by,

F = (u/r).N
where u is the coefficient of roling friction (which has the dimension of length)
r is the radius of the rolling object
N is the normal reaction.

You may refer to the following web-page:

http://www.tutorvista.com/content/physics/physics-iii/motion-laws/rolling-friction.php

維基百科的內容不常是想像中般淺顯，通常不大適合入門。