Under comparable conditions, which of the following types of friction is…

Concept

Friction is a contact force that opposes relative motion, or the tendency of relative motion, between surfaces.

The instantaneous static-friction force is self-adjusting and can be zero. In the standard comparison of contact modes under the same load, materials, and surface condition, the relevant ordering is limiting static friction > sliding friction > rolling resistance.

Application

The stem now specifies comparable conditions. Rolling replaces continuous sliding at the contact with rotation and localized deformation, so its energy loss and resistance are lower than those of sliding friction and limiting static friction.

Contrast

• Sliding friction involves continuous relative motion and appreciable shearing of microscopic surface irregularities.

• Static friction adjusts to prevent motion and may rise to its limiting value before slipping begins.

• “More than one of the above” would require a tie at the minimum, whereas the standard contact-mode ordering is strict.

• “None of the above” would require the minimum to lie outside the listed types, whereas the standard ordering includes its minimum within the list.

Cross-check

Wheels and ball bearings replace sliding with rolling because rolling offers much less resistance under comparable conditions.

Therefore, rolling friction is generally the least under comparable conditions.