What is another word for rest energy?
Pronunciation: [ɹˈɛst ˈɛnəd͡ʒi] (IPA) 
Rest energy is a term used to describe the energy that an object possesses due to its mass. It is also known as internal energy or rest mass energy. There are several synonyms for this term, including invariant mass, proper mass, and intrinsic mass. Invariant mass refers to the mass of an object that remains constant even as it moves closer to the speed of light. Proper mass is the mass of an object as measured in its own rest frame, while intrinsic mass is a similar concept in quantum mechanics that describes the mass of a particle based on its interactions with other particles. These terms are all closely related and refer to the same underlying concept of the energy that an object possesses due to its mass.
