An interesting question to consider is How many calories do you burn just trying to understand what a calorie is? First of all, we have to establish whether we are talking about Calorie with a capital C or calorie with a lowercase c. A Calorie with a capital C is defined as the amount of energy required to raise the temperature of 1 kilogram of water 1 degree Celsius (°C). Thus, it is a unit of energy equal to approximately 4,000 joules. Calorie with a capital C also goes by the names large calorie, kilocalorie, and kilogram calorie. This is the Calorie that you encounter when reading the cereal box in the morning or in any discussion of your diet. For example, you should read … based on a 2,000 calorie diet as … based on a 2,000 large calorie diet.
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Alternatively, a calorie with a lowercase c is defined as the amount of energy required to raise the temperature of 1 gram of water 1 °C, or approximately 4 joules. Calorie with a lowercase c also goes by the names small calorie and gram calorie. Notice that 1,000 small calories equal 1 large calorie. The small calorie is the calorie that you encounter frequently in chemistry and physics class.
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A precise understanding of calorie, however, requires an understanding of the nature of water. It turns out that the energy required to raise any mass of water 1 °C depends slightly on the temperature of the water. For example, the energy required to raise the temperature of 1 gram of water from 4 °C to 5 °C is 4.2045 joules, and the energy required to raise the temperature of 1 gram of water from 15 °C to 16 °C is 4.1855 joules. To remove this ambiguity, in 1950 the calorie was defined in terms of the joule exactly: 1 small calorie equals 4.184 joules exactly, or 1 large calorie equals 4,184 joules exactly. This definition corresponds closely to the energy required to raise the appropriate mass of water from 14.5 °C to 15.5 °C.
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To answer the original question of this note: a 150 pound person (sitting) has burned approximately 1.5 large calories or 1,500 small calories since beginning to read this note. Work those neurons!
