ok, so a infinitesimal change in entropy is dS = dQ/T. Differentials are used so that temperature change is neglibible over the change in Q. Now, I have a homework problem that wants me to express the change in entropy of a rod as a function of length changes and temperature changes. Now, isn't the change in entropy with respect to change in length zero, since dS = dQ/T??? The internal energy changes wrt work done on the rod, but it seems the entropy does not? Can someone explain why it does change with length changes? Also, if entropy does change wrt length changes how would I go about determining the entropy changes along an integration path where T is constant?? the force on the rod is F = -aT^2(L-Lo), where Lo is the initial length. Thanks a lot.