In thermodynamics, an entropic force is a force resulting from the entropy of a system. It is also known as a dissipative force. The concept was first introduced by Rudolf Clausius in 1850. The entropy of a system increases when it undergoes irreversible processes, such as the flow of heat or the diffusion of matter. As a result, an entropic force acts to oppose these processes and maintain the equilibrium of the system.
The most familiar example of an entropic force is friction. When two bodies rub together, they create heat and disorder (entropy). This opposes the motion of the bodies and eventually brings them to a stop. Other examples include surface tension (the tendency of liquids to minimize their surface area), viscosity (the resistance of fluids to flow), and electrical resistance (the opposition to the flow of electrons).
Entropic forces are responsible for many everyday phenomena, such as why objects fall down instead of up, why water flows downhill, and why solids have rigidity. They play an important role in many technological applications as well, such as brakes and bearings. Understanding and controlling these forces is essential for engineering design and optimization.