The Definition of Heat

       What will happen if you touch a cool wall with your hands for five minutes? Your hands will feel cooler and the parts of the wall that you touch will be warmer. The temperature of your hands decreases while the temperature of the wall increases. The heat energy flows from your warm hands to the cool wall. 

   The energy flowing from an object with higher temperature to another object with lower temperature is called heat. The heat always flows from an object with higher temperature (hot) to another object with lower temperature (cool). You cannot feel cool if you are standing near a fire. 

            Heat is measured in unit of calorie. One calorie is defined as the amount of the heat energy required to raise the temperature of 1 ^oC of  1 gram of water. It will take 500 calories to heat 500 grams of water from 20 ^oC to 21 ^oC. In International System, heat is measured in unit of Joule. One Calorie is equal to  4.184 Joule, and it is frequently rounded up to  4.2 joule.

            Your body converts some food you eat into heat energy. The heat energy provided by the food is measured in Calorie (Kilocalorie). We use kilocalorie for the food to simplify the expression. One kilocalorie (kcal) of food is equal to 1000 calories.

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