damping

Any mechanism that drains energy from an oscillator and brings it eventually to rest. The simplest model is _velocity-proportional_ — a force `−c · ẋ` opposing motion — which makes the equation `m ẍ + c ẋ + k x = 0` linear and easy to solve. Three regimes by how `c` compares to `√(4mk)`: _underdamped_ (oscillates while shrinking), _critically damped_ (returns to rest fastest with no oscillation), _overdamped_ (returns slowly without oscillation). Damping is more general than _drag_ — drag is one specific source (fluid resistance), while damping covers friction, viscous flow, electrical resistance, structural hysteresis, anything that takes the oscillator's energy and never gives it back.