  A balance is described with Langmuir binding of weights to each side. This
simple physical system, when coupled with a previously derived equation for the
equivalent displacement of weight that perturbs the equilibrium of a balance,
models two-state, receptor systems in pharmacology for receptor activation.
Surprisingly, this system also shows desensitization similar to many
drug-receptor systems. Although understanding the biophysics behind receptor
signaling is an important endeavor by itself, this analogy with a simple
balance may bring new insights into other areas of physics as well.
