viscous damping

In physics, viscous damping is a type of damping that restrains vibratory motion by dissipating energy, typically through the movement of a fluid. This occurs when a fluid is forced through a small opening by a piston, as seen in automobile shock absorbers. The force generated by viscous damping is directly proportional to the relative velocity between the two ends of the damping device.1

Viscosity itself is the resistance of a fluid to changes in shape or movement between its neighboring parts, essentially denoting its opposition to flow. Methods for measuring viscosity include observing the damping of torsional oscillations of a disk in a fluid or the effect of the fluid on oscillation frequency. The term "kinetic viscosity" is also used, representing the ratio of shear viscosity to density.23