Thermodynamics
Study large collections of particles through temperature, energy transfer, internal energy, phase, entropy, and the constrained processes that connect macroscopic states.
Many microscopic motions become a few macroscopic state variables.
Thermodynamics compresses an enormous microscopic world into quantities such as temperature, pressure, volume, and internal energy. The interesting question is not only what state a system is in, but which changes are possible and which direction they naturally run.
slower typical microscopic motion
faster typical microscopic motion
Follow energy from state to direction.
Hover or focus a stage and the surrounding particle field retunes to that idea. The laws appear where they become useful rather than acting as the table of contents.
It is not heat and it is not the total energy stored by an object. It helps describe the distribution of microscopic energy.
Heat names transfer driven by a temperature difference. Once transferred, that energy contributes to the receiving system's internal energy.
Energy conservation says what balances. Entropy adds a statistical constraint on which macroscopic changes are overwhelmingly favored.