Overview

It’s the study of energy. How to move it, how to store it, and why you can’t ever break even. It governs everything from car engines to black holes.

Core Idea

Entropy: A measure of disorder. The Second Law of Thermodynamics states that the total entropy of an isolated system can never decrease over time. Things naturally fall apart; they don’t naturally come together.

Formal Definition (if applicable)

First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed. $\Delta U = Q - W$ (Change in internal energy = Heat added - Work done).

Intuition

  • First Law: You can’t win. (Energy is conserved).
  • Second Law: You can’t break even. (You always lose some energy to heat/entropy).
  • Third Law: You can’t get out of the game. (You can’t reach absolute zero).

Examples

  • Heat Engine: Converting heat into work (e.g., a steam engine or internal combustion engine).
  • Refrigerator: Using work to move heat from a cold place to a hot place (fighting nature).
  • Perpetual Motion Machine: Impossible because of the laws of thermodynamics.

Common Misconceptions

  • “Heat rises.” (Hot air rises because it is less dense. Heat itself radiates in all directions.)
  • “Entropy is just ‘messiness’.” (It’s more accurately about the number of possible microscopic configurations a system can have.)
  • Enthalpy: Total heat content of a system.
  • Carnot Cycle: The theoretical most efficient heat engine possible.
  • Heat Transfer: Conduction, Convection, Radiation.

Applications

  • Power Plants: Generating electricity.
  • HVAC: Heating and cooling buildings.
  • Chemical Engineering: Designing reactors.

Criticism / Limitations

Classical thermodynamics deals with macroscopic systems in equilibrium. It doesn’t describe microscopic details or non-equilibrium states well (requires Statistical Mechanics).

Further Reading

  • Fermi, Thermodynamics
  • Cengel & Boles, Thermodynamics: An Engineering Approach