The Restless universe | ||||

Introduction to The restless Universe 1 The lawful Universe 3 The irreversible Universe 3.1 Thermodynamics and entropy 1/3 3.1 Thermodynamics and entropy 2/3
3.2 Equilibrium and irreversibility 1/2 3.2 Equilibrium and irreversibility 2/2 -------------------- Other titles in the Physical World series | 3 The irreversible Universe3.1 Thermodynamics and entropy Part 1 of 3 | Part 2 | Part 3 For a printable version of '3 The irreversible Universe' click here , and that a small amount of heat T is transferred from the steak to the plate. Q
while the entropy of the plate increases by Q/T0.95Q/. It is easy to see that the entropy lost by the steak is smaller than the entropy gained by the plate, so the total entropy of the Universe has increased; this process is therefore consistent with the second law of thermodynamics. If, on the other hand, heat T had flowed from the cold plate to the hot steak, the entropy lost by the plate (Q0.95Q/) would have been greater than the entropy gained by the steak (T), and the total entropy of the Universe would have decreased. This violates the second law of thermodynamics, so we can be sure that the process is impossible. Heat flow is said to be an Q/Tirreversible process - you will never see heat flowing spontaneously from a cold body to a hotter one.Whenever energy is transferred or transformed, the final entropy of the Universe must be at least as high as the initial entropy. This usually means that heat flows are required to ensure that the total entropy does not decrease. Inventors should again take note. In most engines, heat is an unwanted by-product: the real aim is to transfer energy as work, perhaps to propel a vehicle or lift a weight. Since part of the energy initially stored in the fuel is inevitably wasted as heat, only a fraction is left to do useful work. Thus, thermodynamics imposes fundamental limits on the
Continue on to 3.2 Equilibrium and irreversibility, part 1 of 2 | Relevant Links A note on powers of ten and significant figures Suggestions for further reading | ||

S207 The Physical World | ||||