calorie cal
example, if you hold an ice cube in your hand, the ice cube slowly melts as energy in the form of heat is transferred from your hand to the ice. As your hand loses energy, it starts to feel cold. Because of their interrelationships, energy, work, and heat have the same units. The SI unit of energy, work, and heat is the joule J . A joule is a tiny amount of energy. For example, it takes about 4 J to warm 1 mL of H2O by 1C. Many processes occur with energy changes in thousands of joules, so the kilojoule kJ is also common. Another unit of energy, used widely in the health professions and everyday life, is the calorie cal . The calorie was initially defined as the amount of energy needed to warm 1 g of H2O by 1C, but in modern times, the calorie is related directly to the joule, as follows: 1 cal = 4.184 J We can use this relationship to convert quantities of energy, work, or heat from one unit to another. The calorie is used in nutrition to express the energy content of foods. However, because a calorie is a rather small quantity, nutritional energies are usually expressed in kilocalories kcal , also called Calories capitalized; Cal . For example, a candy bar may provide 120 Cal nutritional calories of energy, which is equal to 120,000 cal. Proteins and carbohydrates supply 4 kcal/g, while fat supplies 9 kcal/g.