Internal energy of a system in thermodynamic equilibrium (see thermodynamics) by virtue of its temperature. A hot body has more thermal energy than a similar cold body, but a large tub of cold water may have more thermal energy than a cup of boiling water. Thermal energy can be transferred from one body, usually hotter, to a second body, usually colder, in three ways: conduction (see thermal conduction), convection, and radiation.

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