This is from 101 Things I Learned in Engineering School dealing with “equilibrium is a dynamic, not static, state”.

When two chemicals come in contact and react, the reaction often appears to stop after a period of time as an equilibrium is reached. Some portions of the chemicals will have combined into a new chemical product, while other portions appear unaffected. But even in equilibrium, the mixture often remains active, as portions of the product “uncombine” into the reactants and reactants continue combining into new product. However, the overall crossover rates balance and there is not net change in the system.

A structural equilibrium is similarly dynamic. A structural element, even though at rest, works quietly and unceasingly to resolve the various forces acting on it into an overall force of zero. Without the zeroing of forces, an object will accelerate, decelerate, or change direction.

This is how economists ought to teach equilibrium, as an ongoing market tension with forces of all kinds continuing to attempt to reshape everything you see. Equilibrium should not be taught as stability. It should not be taught as a position of rest, whatever might be the appearance at some superficial level.

Economists teach equilibrium as a state of rest. We do it in micro with supply and demand. We do it in macro with aggregate supply and aggregate demand. The following video – which perfectly states the economist’s view – shows how equilibrium is taught in discussing a single market for a single product.

We say, of course, that all other things must be equal for the equilibrium to be maintained, but we do not go on to say that in no market are other things ever actually equal, that the entire notion of equilibrium is a fiction, perhaps a useful fiction, but a fiction all the same. In economics we stress stability when the actual world is anything but.