Re:Excuse me? (Score 5, Informative)

...and furthermore the equilibrium is stable...

Did you think, at all, before you wrote that? What do you think "equilibrium" means?

In dynamics, an equilibrium point is a steady-state of the system: that is, a set of values for the system such that, if the system is set to that point, the system will no longer change.

What do you think "stable" means?

In this context, "stable" means that, if you move the system slightly away from the equilibrium point, it will naturally move back to the equilibrium point. On the other hand, an unstable system, when perturbed from the equilibrium point, will not return to that point.

So, for example, the point of an inverted cone is an unstable equilibrium point. I can balance a ball on it, and it won't go anywhere; but move it ever-so-slightly, and it will fall down. On the other hand, the bottom of a conical pit is stable; move the ball anywhere up from the bottom, and it will just fall back down again.

These are basic definitions for this sort of mathematics. It probably wouldn't hurt, under the circumstances, to assume the author knows what's he talking about, you know.