Static friction is the friction between two surfaces that are not moving relative to each other. It is the force that prevents an object from slipping when it is placed on a surface. The coefficient of static friction is the ratio of the force required to start an object moving on a surface to the normal force between the two surfaces. Static friction is typically greater than kinetic friction.
Kinetic friction is the friction between two surfaces that are moving relative to each other. It is the force that opposes the motion of an object when it is sliding on a surface. The coefficient of kinetic friction is the ratio of the force required to keep an object moving on a surface to the normal force between the two surfaces. Kinetic friction is typically less than static friction.
Rolling friction is the friction between a rolling object and a surface. It is the force that opposes the rolling motion of an object. The coefficient of rolling friction is the ratio of the force required to roll an object on a surface to the normal force between the two surfaces. Rolling friction is typically much less than static or kinetic friction.
