E =mc2 - continued
We see from this consideration of conservation of momentum that as the energy of an object increases, its mass increases.
Einstein showed in 1905 that this is the whole story! Energy is mass -- mass is energy. In his words, “the mass of a body is a measure of its energy content”.
The mass in E=mc2 is the relativistic mass , i.e. ? times the rest mass m0.
The most famous equation in modern science! Energy and mass are equivalent!