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Even though it has been over 150 years since the First Law of Thermodynamics was discovered, we still find that heat is misunderstood. For example, the many environmental science textbooks define heat as "the total kinetic energy of atoms or molecules in a substance not associated with bulk motion of the substance." THIS IS WRONG! What these books are describing is the thermal energy of a system. This is a common misconception. While heat is energy, it is not a containable form of energy since, by its very definition, heat is energy that is transferred. In particular, heat is the energy transferred between objects of different temperature. The misunderstanding comes from the fact that we often talk about heat leaving or entering an object, which gives people the idea that the object must contain heat. But this is not the case. Once heat enters an object, it increases the internal energy of an object, which is the same result that doing work on the object would produce. The object does not contain the heat or the work; it merely changes its energy because of them.