[in Japanese]

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Formerly we researched the general characteristics of the rolling friction by using rollers and bearings made of steel and glass, and found that the moment of dynamical solid friction M_f, within the elastic limit and when the surface roughness was less than 1 μ, was proportional to the contact area given by Hertz's contact theory.
But this time we have measured the rolling friction of steel ball (in steel and glass bearings) by gravitational pendulum method. And the results newely obtained are all the same with the general characteristics of friction of roller, and are as follows.
1) Within the elastic limit and if surface is very smooth, M_f is proportional to the contact area and is given by the following formula.
M_f=cSr₁ (dynecm)
where, c : the frictional force per unit area (dyne/cm²)
S: the contact area given by Hertz's contact theory (cm²)
r₁: radius of ball (cm)
From our experiment, the value of c was 33.27×10³ dyne/cm².
2) However, in case the small ball is loaded by comparatively heavy load (within the elastic limit), M_f increases deviating from the above-mentioned relation, and it is not yet clear whether this phenomenon is due to the strain at the contact part, the surface roughness, or due to other causes.
3) It is considered that beyond the elastic limit M_f is proportional to P^3/2 (P : total load) and independent of radius of ball.

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