Rest energy refers to the energy that an object possesses due to its mass, even when it is at rest (i.e., not moving). This concept is a fundamental aspect of Einstein's theory of special relativity.
According to Albert Einstein's famous equation, E = mc^2, where: E = energy, m = mass of the object, and c = the speed of light in a vacuum (approximately 299,792,458 meters per second).
The equation shows that mass and energy are interchangeable. Even when an object is not moving (its velocity is zero), it still possesses energy due to its mass. This energy is called rest energy because it is the energy the object has when it is "at rest" or not undergoing any motion.
The concept of rest energy is particularly important in understanding nuclear reactions and the behavior of subatomic particles. In nuclear reactions, a small amount of mass can be converted into a large amount of energy, as seen in nuclear fission and fusion processes. The rest energy of an atomic nucleus can be significant compared to the energy released during these reactions.
For example, the rest energy of a single electron is on the order of 511 keV (kilo-electron volts), which is the same amount of energy that would be released if the electron were to annihilate with a positron (its antiparticle). Similarly, the rest energy of a proton is on the order of 938 MeV (mega-electron volts).
In summary, rest energy is the energy inherent in an object by virtue of its mass, as described by Einstein's famous equation E = mc^2. It plays a crucial role in understanding the relationship between mass and energy and has significant implications in various areas of physics, particularly in the realm of particle physics and nuclear reactions.