component along contact plane of contact force for slipping surfaces +, force that slows down slipping of surfaces in contact +, retarding force for contact surfaces slipping +
component of contact force orthogonal to surface of contact +, component of contact force perpendicular to contact surface +, force preventing objects from going into each other +, …
component along contact plane of contact force for contact surfaces in rest +, force opposing slipping tendency for contact surfaces in rest +, force that prevents surfaces in contact from slipping +