Internal energy refers to the sum of kinetic and potential energies of particles within a system. Synonyms for internal energy include thermal energy, heat energy, and the total energy of a system. Heat energy represents the transfer of internal energy from one body or system to another. It is a form of energy that can be sensed and measured. Thermal energy is also a synonym for internal energy. This type of energy is generated by thermal motion, meaning the movement of particles within a system. Additionally, the total energy of a system can be used as a synonym for internal energy, as it represents the sum of all potential and kinetic energy of a system.