1.3 First Axiom of Thermodynamics

 (1.2)

 $\delta Q$: heat energynot!! heat stuff: A scientific letter of the 19. century: Blacksmith uses a hammer to form metal; the metal gets warm; the heat stuff flows from the hand into the metal; as a consequence the hand and the head of the blacksmith become cold!
• energy is conserved
• not force (as was successfully introduced by Newton’s mechanics $F=ma$) but energy is the new fundamental concept of physics
• which force belongs to the heat energy? (later)

Example:

 ${U}_{2}-{U}_{1}=Q-W$ (1.3)

p.s. $pV$-diagrams have been a company secret of James Watt for several years.
Thus he had a monopoly for good heat transforming machines.