Chap. 15: the Laws of Thermodynamics 0)If two objects are in thermal equilibrium with a third, they are in equilibrium with each other 1) There is a quantity known as internal energy that in an isolated system always remains the same 2) There is a quantity known as entropy that in a closed system always remains the same(reversible)or increases(irreversible) Physics 121: Lecture 25, Pg 11Physics 121: Lecture 25, Pg 11 Chap. 15: the Laws of Thermodynamics 0) If two objects are in thermal equilibrium with a third, they are in equilibrium with each other. 1) There is a quantity known as internal energy that in an isolated system always remains the same. 2) There is a quantity known as entropy that in a closed system always remains the same (reversible) or increases (irreversible)