Formula: Rolling Friction Force    Rolling friction coefficient

Rolling friction force

Unit
Force that acts against the motion of the body being rolled on a rough surface.

Normal force

Unit
Normal force is the force exerted on the body by the surface on which the body is placed. In this way the body does not simply fall through the surface. The normal force acts perpendicular to the surface on which the body is placed.

"Normal" is meant in the geometric sense and means "orthogonal". You could also call the normal force an orthogonal force.

Rolling friction coefficient

Unit
Rolling friction coefficient is here the proportionality constant between the rolling friction force $$F_{\text r}$$ and the normal force $$F_{\text N}$$. The larger the rolling friction coefficient is, the more difficult it is to roll the body on the surface.

Surfaces Rolling friction coefficient $$\class{red}{\mu_{\text r}}$$
Car tire on asphalt0.011 bis 0.015
Railroad wheel on rail0.001 bis 0.002
Car tire on concrete0.01 bis 0.02
Car tire on sand0.2 bis 0.4
Rolling friction coefficient for some surfaces.

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