Momentum and Energy


How is energy measured?

The SI unit for energy is the joule (J), but energy is often measured in other units. The calorie (cal) and the kilo-calorie (kcal) or food calorie are used both for chemical energy stored in foods and to measure heat. The British Thermal Unit (BTU) is most often used to measure heat in homes and industries. The kilowatt-hour (kWh) is used to measure electrical energy. A completely unofficial, but useful unit is the jelly doughnut (JD), the energy in a medium-sized jelly-filled doughnut. It helps relate all these units to a tasty treat. The table below illustrates conversions among the units. To use it read across. For example, 1 J = 0.239 cal, 1 cal = 4.186 J, 1 JD = 239 kcal.


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