What is the difference between energy and relativistic mass?

[dreamfly]

In the modern interpretation, m is the "invariant mass" of an object, and the equation E=mc^2 holds only in the rest system.

is the rest system to viewer?

 

[jtbell]

is the rest system to viewer?

I'm pretty sure Meir meant "the rest system of the object in question."

In the usual modern terminology the energy of an object is

$$E = \frac {mc^2}{\sqrt {1 - u^2 / c^2}}$$

where $u$ is the speed of the object in whatever reference frame you're working in, and $m$ is the invariant mass, which is often called the "rest mass". This reduces to $E = mc^2$ when $u = 0$, i.e. when the object is at rest.

 

[dreamfly]

I'm pretty sure Meir meant "the rest system of the object in question."

In the usual modern terminology the energy of an object is

$$E = \frac {mc^2}{\sqrt {1 - u^2 / c^2}}$$

where $u$ is the speed of the object in whatever reference frame you're working in, and $m$ is the invariant mass, which is often called the "rest mass". This reduces to $E = mc^2$ when $u = 0$, i.e. when the object is at rest.

Thank you!