Friction is the resistance that one surface encounters when it moves over another. It is the product of fundamental electromagnetic forces, and it occurs among both solid and fluid substances. There are three fundamental laws that dictate the force of sliding friction. All forms of friction convert kinetic energy to heat.
Friction is the resisting force between surfaces. There is friction between different types of surfaces. Dry friction is the lateral friction between two solid surfaces in contact. It is subdivided into static friction, which is friction among non-moving surfaces, and kinetic friction, or friction between moving surfaces.
Fluid friction is the friction between viscous materials moving against each other. Internal friction is the resisting force between the elements that make up a solid material while it undergoes deformation.
Friction produces heat from kinetic energy. This is visible when a person makes fire by rubbing two sticks of wood together. Friction also produces heat in kinetic liquids, as is the case when a person stores a viscous fluid.
The Laws of Dry Friction, discovered between the 15th and 18th centuries, are used to determine the force of friction within a system. Amonton's First Law dictates that friction is directly proportional to applied load. Amonton's Second Law states that the force of friction is independent of the area of contact. Coulomb's Law of Friction stipulates that kinetic friction is independent of the sliding velocity.