In: Physics
The freely jointed chain picture is a simplification of the real physics of a polymer: Actually, the joints are not quite free. Each polymer molecule consists of a chain of identical individual units, which stack best in a straight line (or in a helix with a straight axis). Thus the equations we saw in class say that bending the chain into a tangle costs energy. And yet, a rubber band certainly can do work on the outside world as it retracts. Reconcile these observations qualitatively: Where does the energy needed to do mechanical work come from?