ABSTRACT
Consider an experiment in which all the students in your class line up against the walls of the classroom, half on one side and half on the other. Then consider what would happen when one student on each side walks to the opposite side at exactly the same speed, passing each other in the middle. As soon as each of these students arrives at the other side, another student walks back to the opposite side, continuing at the same speed. Now imagine continuing this process indefinitely. It would be a very dynamic process, two students always moving from one side to the other in opposite directions, but there would never be any net change in the count of students on each side. If we were unable to see the students walking and were only able to count the number of students in the lines, we would never know that anything was happening. This is an example of what is known as equilibrium.
