Coulomb friction

Coulomb friction is a dry-friction model in which friction opposes relative motion and its magnitude is proportional to the normal force, largely independent of sliding speed.

Static friction: Friction that prevents relative motion between surfaces up to a limiting force. Below the limiting force, the model permits contact to stick rather than slide.
Leonardo da Vinci: An Italian Renaissance artist, engineer, and investigator of mechanics. His notes record early experiments identifying regularities in dry friction.
Friction brake: A brake that slows motion by pressing surfaces together and dissipating energy through friction. Brake torque is commonly estimated from contact load and a friction coefficient.
Stribeck effect: The decrease in friction with increasing speed over a low-speed range in some lubricated contacts. It contradicts the model's assumption that sliding friction is largely speed-independent.
Kinetic friction: Friction opposing surfaces that are sliding relative to one another. During sliding, Coulomb friction sets its magnitude from the normal force.
Guillaume Amontons: A French physicist whose experiments helped establish empirical laws of dry friction. His 1699 work revived the proportionality between friction and normal load.
Belt friction: The frictional interaction between a belt and a wrapped surface or pulley. Coulomb friction underlies the capstan relation used to estimate belt tension ratios.
Viscous friction: Resistance to motion proportional to velocity, commonly produced by fluid drag or lubrication. Its force varies with speed, unlike ideal Coulomb sliding friction.
Normal force: The contact force perpendicular to two touching surfaces. It supplies the proportional quantity that sets the model's friction magnitude.
Charles-Augustin de Coulomb: A French physicist and engineer known for work on electrostatics, mechanics, and materials. His 1785 friction study developed the laws that gave the model its name.

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