**Departures From the Steady State**

Now, what will happen if we change some part of this system? Will
the steady state be permanently or temporarily disrupted? One of the
real beauties of STELLA is that it makes it so easy to answer these
kinds of "what if..." questions. Think about what might happen if we
changed the initial amount in the water tub from 10 to 5 liters. What
if we changed the initial amount to 15 liters? Make predictions for
both of these cases an then implement the changes in your model by
double-clicking on the water tub icon and changing the initial value.
When you run the model with these new starting conditions, you should
reproduce the results shown in Figure 2.6 below.

Figure 2.6. The graphs from
Experiments 2 and 3 show the results of changing the initial amount
of water in the tub to 5 liters and then to 15 liters - representing
an initial decrease and increase relative to the previous steady
state level of 10 liters. In both cases, the system responds by
either increasing or decreasing the drain flow rate until the water
tub contains 10 liters again, at which point the system has returned
to it steady state.

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