Kinetic friction is the force that opposes the motion of two surfaces sliding against each other. It occurs when an object, like a box, is in motion on a surface, such as a floor. This force depends on the nature of the surfaces in contact and the normal force pressing them together. The strength of kinetic friction is usually less than static friction, which acts when an object is at rest. The coefficient of kinetic friction is a value that helps quantify this force, allowing us to predict how easily an object will slide across a surface.