Work, Heat, and Energy
Energy is defined as the capacity to do work. Because energy appears in many forms (kinetic, thermal, electrical), different industries have created highly specialized units to measure it.
The Standard and the Dietary
- Joule (J): The SI unit of energy. Lifting a small apple one meter takes about 1 Joule.
- Calorie (cal): The energy needed to raise 1 gram of water by 1°C.
- Kilocalorie (kcal or Food Calorie): The standard "Calorie" seen on nutrition labels is actually 1,000 thermal calories (4,184 Joules).
Electricity and Buildings
- Kilowatt-hour (kWh): Used on electrical bills, representing a power of 1,000 Watts sustained for one hour (3.6 Megajoules).
- BTU (British Thermal Unit): Widely used in HVAC industries to rate air conditioners and furnaces.
Scientific and Destructive
- Electronvolt (eV): Used in particle physics, the amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt.
- Ton of TNT: Used to measure the energy yield of explosive and nuclear weapons. Represents 4.184 Gigajoules.