A lubricant is a substance used to facilitate the relative motion of solid bodies by minimizing friction and wear between interacting surfaces.
Lubricants are classified into two categories :
Internal Lubricants: It reduces friction between the molecular chains.
External Lubricants: They reduce the adherence between polymer melt and metal surfaces.
Friction is a force between two surfaces that are sliding, or trying to slide, across each other.
Friction always works in the direction opposite to the direction in which the object is moving or trying to move.
Some examples of friction are - pushing a book along the floor, rubbing both hands together to create heat, Skis sliding against snow, and iron being pushed across the material, etc.