Friction is a force between two surfaces that are sliding, or trying to slide, across each other. For example, when you try to push a book along the floor, friction makes this problematic. Friction works in the direction opposite to the direction in which the object is moving or trying to move. It is not a fundamental force, like gravity or electromagnetism. Instead, scientists believe it is the result of the electromagnetic attraction between charged particles in two touching surfaces. When an object is moving, the friction is proportional and perpendicular to the normal force (N) Friction is independent of the area of contact so long as there is an area of contact. The coefficient of static friction is slightly more significant than the coefficient of kinetic friction.