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Answers
Static friction operates between two surfaces that aren't moving relative to each other, while kinetic friction acts between objects in motion. In liquids, friction is the resistance between moving layers of a fluid, which is also known as viscosity.
Sliding friction (also called kinetic friction) is a contact force that resists the sliding motion of two objects or an object and a surface. ... μ k is the coefficient of kinetic friction, and N is the normal force.
Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. ... In analogy with sliding friction, rolling resistance is often expressed as a coefficient times the normal force.