THERMODYNAMICS

The air molecules around you right now are moving at about 500 meters per second — faster than most bullets. Yet you don’t feel a thing, because each molecule is unimaginably tiny and collides with its neighbours billions of times per second. Kinetic theory explains how this invisible chaos creates everything you can measure: pressure is just trillions of molecular impacts per second, temperature is just how fast the molecules are moving, and the ideal gas law PV = nRT falls straight out of Newton’s laws applied to bouncing particles.

Energy is the most fundamental concept in physics — a conserved quantity that never changes in an isolated system. This guide covers kinetic energy, potential energy, conservation of energy, Noether’s theorem, E=mc², and every major energy form with clear explanations, formulas, and an interactive simulation.

Every system — from engines to the human body — follows a simple rule: energy in equals energy out. This is the first law of thermodynamics, expressed as ΔU = Q − W, where changes in internal energy depend on heat added and work done. Though simple in principle, it explains everything from why engines need fuel to why perpetual motion machines are impossible, shaping how energy flows through the physical world.