Coulomb friction acts along the plane of contact between two solid surfaces, in opposition to their actual or potential relative motion, and in proportion to the normal force pushing the surfaces together. It encompasses both kinetic friction, applied when the surfaces are in relative motion, and static friction, applied when they are locked together. Coulomb friction is the basis for clutches and clutch-like elements that rely on normal forces to keep surfaces in contact. When the relative speed of the surfaces becomes small enough and a normal force is applied, these elements lock and move together.
Realistic friction models often include viscous friction. This type of frictional force or torque is proportional to the relative translational or rotational velocity of the two surfaces in contact.
The Clutches library contains various clutch types, including single- and multi-plate, friction, cone, and dog (positive) clutches. You can customize the fundamental clutch blocks to meet your requirements. The Brakes & Detents library provides brake, detent, and friction blocks. These clutch-like elements apply Coulomb friction forces or torques between pairs of translating or rotating axes in loaded contact. Many also allow inclusion of viscous friction. Once engaged, clutches and brakes act to decelerate the relative motion of surfaces in contact and can lock the surfaces together under certain conditions.
Clutches and clutch-like elements have a dual role in a driveline model. When engaged but not locked, they act as dynamic elements, generating torques and forces between driveline axes in relative motion. When locked, they act as conditional or dynamic constraints, locking driveline axes to move together. Such constraints are conditional, because they can unlock, unlike gears.