 Welcome back, we remember our first law the final form as q equals delta e plus w. I can transpose this by writing it as delta e is q minus w. And if we expand delta e and if we expand w, we will notice that delta e can be expanded into delta u plus delta e potential plus delta e kinetic plus many other modes which equals q minus let us split w into the possible modes expansion work done by stirring electrical work plus many other modes. Now we know that this is a long equation with a large number of terms but it is a single equation and a single equation can be solved only for a single quantity. So suppose there are 12 significant terms here, 11 need to be specified so that the 12th can be determined. Not a very attractive situation, that is one point. Second point is we have kept delta u in the forefront of the expansion of delta e because for us mechanical engineers this is likely to be the most significant of the components of delta e. Now we know that delta u is the thermal energy of the final state minus the thermal energy of the initial state. But we are yet to answer this question, how does u depend on other properties of the system? Because unless we relate u to other properties of the system, the concept of u is not really very useful. What we are going to do now is to slowly look at 0th law, bring in the concept of temperature and then see the way in which the thermal energy u is related to temperature. Thank you.