dissipation

Dissipation is the process by which energy within a physical system is transformed and dispersed into less useful forms, typically as heat, and spread into the environment. The term conveys irreversibility: energy that can no longer be fully recovered to perform work is said to have dissipated.

In thermodynamics, dissipation describes irreversible processes that increase entropy and reduce the availability of energy. Mechanisms include viscous dissipation in fluids, heat conduction, friction, and inelastic deformation. The second law of thermodynamics implies that the total entropy of an isolated system does not decrease, with dissipation as a primary mode by which energy becomes less accessible for work.

Mechanical and electrical examples: In mechanics, viscous damping converts kinetic energy into heat, while inelastic collisions dissipate kinetic energy. In electrical circuits, resistors dissipate electrical energy as heat, P = I^2R. In fluid dynamics, viscous dissipation converts macroscopic flow energy into internal energy, raising temperature slightly.

The concept also enters theoretical formalisms: a dissipation function or dissipation potential can describe irreversible contributions to the rate of change of a system’s state in continuum mechanics; in quantum mechanics, coupling to an environment produces dissipation and decoherence, often modeled by open-system dynamics.

Practical considerations: dissipation affects the efficiency of engines and energy conversion devices, electronic components, wave propagation, and signal processing. Engineers seek to minimize unwanted dissipation to improve efficiency, while controlled dissipation can stabilize systems or enable energy harvesting and thermal management.