If water comes into a leaky bathtub at a constant rate and leaks out a rate proportional to the height of the water in the tub, then an equilibrium depth of water in the tub can be reached. You can use this applet to explore how the equilibrium depth depends on the rate of flow into and the rate of flow out of the tub. Clearly, the leaky bathtub is a metaphor for many equilibrium situations that arise because of competing rates. Can you think of others? You can watch an animation by clicking on the "play" icon in the lower left hand corner of either window.