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 .