# Relativistic energy

#### Honorable_Death

can anyone explain to me wha relativistic is?

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Honorable_Death said:
can anyone explain to me wha relativistic is?
It means "obeying the Lorentz transformation" which is necessary if your physics covers different inertial frames (as for example, a fast moving subatomic particle and a lab apparatus assumed at rest). This means that energy depends on relative speed.

#### Honorable_Death

wow sorry i dont no what was wit me when i wrote that forum, but what i ment to ask was can anyone explain to me what relativistic energy is?

#### pmb_phy

Honorable_Death said:
wow sorry i dont no what was wit me when i wrote that forum, but what i ment to ask was can anyone explain to me what relativistic energy is?
Seems to me that when someone is using that term they are referring to the sum of kinetic energy + rest mass energy.

Pete

#### El Hombre Invisible

That's just energy isn't it?

#### pmb_phy

El Hombre Invisible said:
That's just energy isn't it?
Energy (sometimes referred to as "total energy") is an undefined quantity. Its a number associated with a system and this number is a constant. Energy is made up of various forms of energy each of which are well defined. One form is kinetic energy, one is mass-energy, one is potential energy etc. The quantity

E = K + E0

may be what you're thinking of as "relativistic energy." I can't say for sure because I don't know where you got this term. These terms can have different meanings between different authors. I refer to E as "inertial energy." The quantity W defined as

W = E + U

where U is a function of the position of the particle. W is referred to as the total energy of the particle in, say, and electric field. I don't recall ever seening the term "relativistic energy" anywhere. However I've read so much I may have forgotten I've seen it.

Pete

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#### El Hombre Invisible

Relativistic energy due to observable differences in total energy due to differing reference frames. The total energy of an object is given by the root of (pc)^2 + (mc)^2, so relativistic energy is dependant on momentum, which may change frame to frame.

#### pmb_phy

El Hombre Invisible said:
Relativistic energy due to observable differences in total energy due to differing reference frames. The total energy of an object is given by the root of (pc)^2 + (mc)^2, so relativistic energy is dependant on momentum, which may change frame to frame.
That's true so long as the body is not under stress and has zero potential of position.

Pete

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