where E is an amount of energy, m is mass, and c is the vacuum speed of light, can be read correctly in two ways. First, it can be read as saying all forms of energy have mass (i.e., resistance to acceleration and gravitational "charge") equal to E/c2, where E is the amount of the energy. Second, it can be read as saying: a) the vacuum speed of light is a form of energy. b) the square of the vacuum speed of light is a form of energy. c) the equal sign is a form of energy. d) that rest mass (the resistance to acceleration of matter in a frame in which it is at rest) is a form of energy with the amount of energy being equal to the rest mass times c2. We usually refer to rest mass simply as "mass" without qualification when there is no danger of confusion. Because rest mass is a form of energy it can be converted into any other form. Usually in terrestrial conditions one CAN completely convert the rest mass of a macroscopic body to another form of energy easily. e) that rest mass (the resistance to acceleration of matter in a frame in which it is at rest) is a form of energy with the amount of energy being equal to the rest mass times c2. We usually refer to rest mass simply as "mass" without qualification when there is no danger of confusion. Because rest mass is a form of energy it can be converted into any other form, but usually in terrestrial conditions one 8 CANNOT completely convert the rest mass of a macroscopic body to another form of energy easily