Friction is the force that opposes the relative motion or tendency toward such motion of two surfaces in contact. It is not a fundamental force, as it is made up of electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or heat. Friction between solid objects and fluids (gases or liquids) is called drag. Friction in an electronic circuit is called resistance. Contrary to popular belief, sliding friction is not caused by surface roughness, but by chemical bonding between the surfaces - by the stickiness of the two surfaces.