# About Relativistic Mass-Energy Equivalence

While I was looking up E=mc$^{2}$, I have learned such formula only applies to stationary objects and for kinetic object, the formula is this:
E$_{r}$=$\sqrt{(m_{0}c^{2})^{2}+(pc)^{2}}$
Where E$_{r}$ is relativistic energy
and m$_{0}$ is rest mass

In the formula, what is p and what is (pc)$^{2}$?
Also, does the relativistic energy calculated here becomes relativistic mass of the object using E=mc$^{2}$?

## Answers and Replies

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bcrowell
Staff Emeritus
In the formula, what is p and what is (pc)$^{2}$?
Also, does the relativistic energy calculated here becomes relativistic mass of the object using E=mc$^{2}$?
Here E is called the mass-energy of the object, and m is simply called its mass. The interpretation of $E=mc^{2}$ is that when the object is not moving (has zero momentum), the only mass-energy it has is the mass-energy due to its mass.
The term "relativistic mass" is not used any more. Back when people used to use it, it meant the mass multiplied by a factor of $\gamma$.