According to my text book... Thermal energy is the kinetic energy of the component particles of an object and is measured in joules. Heat is the thermal energy that is absorbed, given up or transferred from one object to another. But later on the book there is a small chapter called THERMAL ENERGY (HEAT) and it says... "Students should understand that the term thermal energy refers to the non-mechanical transfer of energy between a system and its surroundings." ⓒ IBO 2007 I thought heat is the transfer of thermal energy but all of sudden it says thermal energy is also a transfer of energy. So what is the difference between thermal energy and heat then?