Energy Conservation & Transformation

Mechanical energy, heat, and the first law of thermodynamics

The Law of Conservation of Energy states that energy cannot be created or destroyed, only transformed from one form to another. In mechanical systems (no friction), kinetic energy (KE = ½mv²) and gravitational potential energy (PE = mgh) continuously convert between each other while their sum stays constant. At the highest point: all PE, no KE. At the lowest point: all KE, no PE. When friction is present, mechanical energy decreases as some converts to thermal energy (heat). The total energy of the universe remains constant — this is the First Law of Thermodynamics (ΔU = Q - W). Perpetual motion machines are impossible because friction always converts some mechanical energy to heat.