Thermodynamics first/second laws
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Definition
1st: Δ U = q - w (energy conserved); 2nd: entropy of universe increases for spontaneous processes.
Thermodynamics first/second laws in plain English
These two laws govern how energy behaves in the entire universe, and they never break. The First Law is basically "you can't create or destroy energy, only move it around": written as Δ U = q - w, it says a system's internal energy changes only by the heat (q) you add and the work (w) it does — a strict accounting ledger where nothing appears from nowhere. The Second Law says that in any process that happens on its own, the total disorder of the universe (called entropy) goes up — which is why a hot coffee always cools to room temperature and never spontaneously reheats itself. Together they explain both why energy is conserved and why time seems to run in one direction: toward more spreading-out and mixing.
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