Kilowatt Hour (kWh)
The kilowatt-hour, symbolized as kWh, is a common unit in electricity billing and energy reporting. It is the energy used by a 1-kilowatt device for 1 hour, or 3.6 million joules. With the advent of electrification in the late 1800s and early 1900s, the kilowatt-hour made measuring electrical energy simpler for both utilities and customers. Its use is crucial for billing, energy management, and understanding electricity use in homes, industry, and renewable energy.
Calorie (cal)
The calorie (cal) originated in the 19th century as a unit for quantifying heat energy. It was initially defined as the energy required to increase the temperature of one gram of water by one degree Celsius under standard atmospheric pressure. The calorie gained popularity in fields such as chemistry, physics, and nutrition. Despite not being an official SI unit, it remains prevalent on nutritional labels and in dietary contexts, particularly in the United States and Europe. Before the widespread adoption of the joule, the calorie played a significant role in standardizing energy measurements related to food and biological systems.