Heat, Energy, and Entropy

The laws of thermodynamics without the dread — energy is conserved, entropy always grows, and that one-way arrow explains heat engines, perpetual-motion failure, and the direction of time.

1. Energy and the First Law Heat is energy in transit, not a substance things contain. Temperature and heat are different. And the first law: energy is never created or destroyed, only moved and reshaped.
2. Entropy and the Second Law Entropy is a count of microscopic arrangements, not mess. The second law says it never decreases in an isolated system — which is why heat flows one way, engines leak, and 'you can't break even.'
3. The Arrow of Time Why time has a direction: entropy. Eggs don't unscramble, the heat-death idea, how Maxwell's demon is defeated, and the honest cost of erasing one bit of information.