Wandwrijving

Wandwrijving, or wall friction, is the frictional force that resists tangential (sliding) motion at the interface between a solid body and a support surface such as a wall. It arises from microscopic surface roughness and intermolecular forces, and it depends on the properties of the contacting materials and the presence of any lubrication or contamination.

In physics, friction at a wall is commonly described by Coulomb’s law of friction. Static friction can adjust up to a maximum value, given by f_static,max = μ_s N, where μ_s is the coefficient of static friction and N is the normal (perpendicular) force pressing the surfaces together. If the tangential force surpasses this limit, the contact enters the kinetic (dynamic) regime, and sliding occurs with a friction force f_kinetic = μ_k N, where μ_k is the coefficient of kinetic friction (typically smaller than μ_s).

A classic scenario is a block of weight W pressed against a vertical wall by a horizontal force F, producing a normal force N ≈ F. The block will not slip downward if μ_s F ≥ W, so the minimum push required for static equilibrium is F_min = W/μ_s. If F is too small, the block slides; in motion, the friction force remains approximately μ_k N opposite to the motion.

Applications of wandwrijving include gripping and supporting objects against vertical surfaces, handholds, clamps, and designing interfaces where friction against a wall contributes to stability. Surface treatment, roughness, cleanliness, and lubrication are important factors affecting the friction coefficient.