Potential energy (PE) is stored energy that can be converted into kinetic energy. The two most common types are gravitational and elastic.
Gravitational PE
PE = mgh, where m = mass (kg), g = 9.81 m/s² (gravity), h = height above reference point (m).
Elastic PE
PE = ½kx², where k = spring constant (N/m), x = displacement from equilibrium.
Conservation of Energy
In a closed system, total energy (KE + PE) remains constant. A roller coaster at the top has max PE; at the bottom, max KE.
Reference Point Matters
Gravitational PE is always relative to a chosen reference height — a book on a table has PE relative to the floor, but different PE relative to the ground floor of the building. Only changes in PE (not the absolute value) are physically meaningful, which is why the reference point can be chosen arbitrarily for convenience.
Everyday Energy Conversion Examples
A stretched bow (elastic PE) converts to an arrow's kinetic energy on release. Water held behind a dam (gravitational PE) converts to kinetic energy, then electrical energy, through hydroelectric turbines — the same PE-to-KE conversion principle scales from playground swings to power grids.