Types of equilibrium

There are essentially three types of equilibrium (or balance): Stable equilibrium, unstable and neutral.

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Think of a golf course. If the golf ball landed in a hollow, if it is disturbed it rolls back again to the bottom of the hollow. The ball is in stable equilibrium.

Whereas if the ball lands up right on top of a small mound at the slightest disturbance it rolls down an example of unstable.

Finally as an example of neutral equilibrium, when it lands on a flat level surface like a table, when moved i.e. rolled it stays there where it now stops.

The ideas would be very well illustrated in a game of put-put.

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To illustrate also imagine a cone (as in ice cream) standing on the base, the (round flat) surface, the equilibrium is stable. If the cone is disturbed and left it falls back and returns to the original state.

Now consider the cone upside down balanced acutely on its point, if the cone is moved just a tiny fraction it falls down. It topples over. It is in unstable equilibrium.

For neutral imagine the cone lying on its side. If it is rolled and moved a bit now it stays like that it doesn't return and it stays in the new position which then doesn't change.

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Of course things are never so simple and you can get more complicated instances and as some combination of these three. There are mathematical descriptions to characterise such situations but this is the basic idea.