Thermodynamics is the study of how particles react and how energy works in a system. There are four facts that hold true in every thermodynamics situation: - If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.

- Heat and work are forms of energy transfer.

- Entropy in a system not in thermal equilibrium increases.

- Entropy in a system approaches a constant as temperature approaches zero.

These ideas are most likely called

a thermodynamics experiment.
a thermodynamics hypothesis.
a theory of thermodynamics.
a law of thermodynamics.