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Mass and energy

Mass and energy are two sides of the same thing. The rest energy of a body is the mass times the speed of light squared. In everyday life we do not notice, because the speed of light is so large that even one gram corresponds to an enormous energy. In nuclear reactions a small difference in mass becomes measurable energy, or the other way round. The conservation law applies to mass and energy together, not to the mass alone when energy leaves the system.

E=mc2E = mc^2rest energy

Symbols

mmmasskg
ccspeed of light, 3.00·10⁸m/s
EErest energyJ

Example

One gram is 0.001 kg. With c=3.00⋅108c = 3.00 \cdot 10^{8} m/s:

E=0.001⋅(3.00⋅108)2=9.00⋅1013E = 0.001 \cdot (3.00 \cdot 10^{8})^2 = 9.00 \cdot 10^{13} J.

The formula does not say that one gram of matter by itself becomes that much heat. The whole mass must be converted.
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