What are the laws of thermodynamics?

The laws of thermodynamics: ΔU = Q − W. Heat always flows from hot to cold by itself, and energy is never lost: heat you put into something either warms it or lets it do work. Because of this, no engine can turn all its heat into work, and nothing can ever be cooled all the way to absolute zero.

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Chapters in this interactive model

1. Heat flows downhill, and the books always balance: Hot meets cold, a heater pushes a piston, and a gas spreads out and never un-spreads.
2. No engine can turn all its heat into work: Carnot’s perfect engine, and the petrol engine in a car.
3. Pushing heat uphill costs work: An AC and a fridge move heat from cold to hot. The second law sets the price.
4. Cold never flows in: heat flows out: Ice in a drink and a pot on the flame. Heat always runs downhill, and entropy always grows.
5. Absolute zero, a clever demon, and a fridge that heats: Why you can never reach 0 K, why sorting molecules isn’t free, and why an open fridge warms the kitchen.