Special theory of relativity (Energy and mass)

In Newtonian mechanics, if a certain amount of force is continuously applied to an object, it gains kinetic energy as given by the following equation:

With regard to the relationship between relative speed and mass, the mass of an object is not constant and increases with its speed and is represented by the following equations:

or

By transforming the equation, we obtain the following equation:

By expanding the denominator , we obtain the following expression:

is small, we can neglect the third and following terms, to obtain the equation:

, then

This equation shows the equivalence of energy and mass.
In practice, a small amount of mass is lost as uranium undergoes nuclear fission, and an enormous amount of energy equivalent to the lost mass is produced.