Energy Over Time
Power is the rate at which energy is generated or consumed (Energy $\div$ Time).
Electrical and Standard
- Watt (W): One Joule of energy per second.
- Kilowatt (kW) & Megawatt (MW): Used to measure engines, power plants, and EV output.
The Age of Steam
- Mechanical Horsepower (hp): Popularized by James Watt to compare his steam engines to draft horses. Equivalent to lifting 33,000 pounds by one foot in one minute (~745.7 Watts).
- Metric Horsepower (PS/CV): Slightly less than mechanical HP (~735.5 Watts). German car manufacturers use PS.
Cooling Power
- Ton of Refrigeration (TR): The power required to freeze exactly one short ton (2,000 lbs) of water into ice in 24 hours. Equivalent to 12,000 BTU/h, representing substantial cooling capacity in large AC systems.