What does friction depend on?

Friction is primarily dependent on the normal force, which is the force exerted perpendicular to the surfaces in contact. The magnitude of the frictional force is influenced by this normal force because the greater the force pressing the two surfaces together, the more microscopic interactions occur between the surfaces, leading to increased friction.

In many cases, friction can be represented by the equation ( F_f = \mu F_n ), where ( F_f ) is the frictional force, ( \mu ) is the coefficient of friction (which depends on the materials in contact), and ( F_n ) is the normal force. This relationship indicates that as the normal force increases, assuming the coefficient of friction remains constant, the frictional force will also increase.

While surface area, relative velocity, and material properties can influence friction, they do not impact it in as direct and significant a manner as the normal force does. The interaction at the surface level triggered by the normal force is what primarily determines the amount of friction generated between two surfaces.