The rest mass also is energy!
When particles are bound together the energy is lower. Examples:
- Earth bound to sun by gravity
- Nucleus of atoms (discussed later in course) is made of particles bound together
If a large weakly bound nucleus can be broken into smaller strongly bound nuclei, energy is released
- Rest mass of nuclei converted to other forms of energy
- Einstein’s prophetic statement: “It is not impossible that with bodies whose energy-content is variable to a high degree (e.g. with radium salts) the theory may be successfully put to the test.”
- The Bomb: conversion of rest mass to kinetic energy:
- Chain reaction
n + U235 -> La139+ Mo95 + 2n + kinetic energy
1 gram of mass = energy released in an atomic bomb