Viscosity

Two trains, going in opposite directions, free-wheel past each other on straight, level, railway tracks. As they do so the passengers throw heavy masses out of their own train and into the other train. This slows the two trains relative to each other.

At a sub-microscopic level an object moving through a fluid might acquire a coating of the fluid adherent to its sides. This coat and the body of the fluid exchange particles by diffusion. By analogy to the trains this tends to slow the relative motion of the body and the fluid.

For a more general mechanism for the slowing of the motion see: Non-Dissipative.

Vis*cos"i*ty (?), n. [Cf. F. viscosit'e, LL. viscositas.]

1.

The quality or state of being viscous.

2. Physics

A quality analogous to that of a viscous fluid, supposed to be caused by internal friction, especially in the case of gases.

© Webster 1913.