Question

What is an example of a stable system?
How were you able to determine whether or not this system is stable?

Answer 1

is a cemented brick wall a stable system?

Answer 2

A stable system is any system that can undergo a perturbation from its equilibrium and then return to that state of equilibrium.

Take the example of a marble in a bowl.

If we lift the marble to the edge of the bowl, we have subjected the system to a perturbation. Once we release the marble, it will roll back and forth and around the bowl. But after enough time, it will return to the bottom of the bowl.

Answer 3

Every system, or I should say most systems, have an envelop of stability, or a given set of conditions where they remain stable.

If I take the marble out of the bowl, this system is no longer stable, in the technical sense.

If we take your cinderblock wall as an example, it is stable under certain conditions but could very well become unstable if we exceed this envelop of stability.

Going with your cinderblock wall, let's examine what forces might act on this wall and whether or not it remains stable in these conditions.

Let's say we built the wall around our house to protect it from the elements.

If it floods, the wall will hold steady and keep the water back. It may deflect slightly from its perfectly upright condition. Once the waters leave, the wall returns to its upright state. The wall is stable.

Now, a hurricane (or typhoon) blows in and blows the wall down. We have exceeded the stability of the envelope and we can no longer consider the system stable because after the hurricane blows over, we don't have a wall left, but instead a pile of cinderblocks!