Energy
The quantitative property that must be transferred to a physical system to perform work on it, or to heat it.
Governing formula
E = mc²
SI unit
J
In depth
Energy is a scalar quantity that is conserved in all closed systems according to the First Law of Thermodynamics. It exists in various forms - kinetic, potential, thermal, chemical, electrical, and nuclear - and can convert between these forms, but cannot be created or destroyed.
Examples in the real world
Chemical energy stored in a battery converting to electrical energy to power a light bulb, or potential energy of water held behind a dam converting to kinetic energy as it flows through turbines.