Thermodynamics
The laws governing heat, energy, and entropy - from steam engines to black holes.
0️⃣ Zeroth Law
If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This foundational law defines what temperature means.
1️⃣ First Law - Conservation of Energy
Energy cannot be created or destroyed, only converted between forms. For a thermodynamic system: ΔU = Q - W (change in internal energy = heat added minus work done by system)
2️⃣ Second Law - Entropy
The total entropy of an isolated system always increases over time. Heat spontaneously flows from hot to cold. No process is 100% efficient at converting heat to work. Entropy always wins.
3️⃣ Third Law - Absolute Zero
As temperature approaches absolute zero (0 K = −273.15°C), the entropy of a perfect crystal approaches zero. Absolute zero is theoretically unreachable but scientists have gotten to within billionths of a degree.
🔄 Carnot Efficiency
The theoretical maximum efficiency of any heat engine: η = 1 − T_cold/T_hot. A nuclear plant with 300°C exhaust and 600°C steam has a max efficiency of ~50%. Real plants are typically 30–35%.
💨 Ideal Gas Law
PV = nRT - Pressure × Volume = moles × gas constant × temperature. Fundamental to understanding heat engines, atmospheres, refrigeration, and more.
🔥 Heat Transfer
Heat moves by three mechanisms: Conduction (contact - metals), Convection (fluid motion - water cooling a nuclear core), Radiation (electromagnetic - the Sun).
📈 Phase Transitions
Changes of state (solid → liquid → gas) occur at constant temperature as energy breaks intermolecular bonds. Latent heat is the energy absorbed or released during a phase change without temperature change.