# E=mc^2 Applied **URL:** \ **Category:** Factual Questions\ **Created:** [October 21, 2003, 3:58am UTC](https://boards.straightdope.com/t/e-mc-2-applied/208638 "2003-10-21T03:58:40Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [October 22, 2003, 4:23pm UTC](https://boards.straightdope.com/t/e-mc-2-applied/208638/21 "2003-10-22T16:23:25Z")
It dpends which propery your looking at **Ring** , in my post above I was careful to say E = mc[sup]2[/sup] relates mass to mass-energy, infact really it should be: E[sub]0[/sub] = m[sub]0[/sub]c[sup]2[/sup]. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 22, 2003, 4:31pm UTC](https://boards.straightdope.com/t/e-mc-2-applied/208638/22 "2003-10-22T16:31:21Z")
> [@](#): > > Good point though. The question works for any unit. To further elaborate, if you used, say, mass measured in slugs, and the speed of light in cubits per fortnight, then you’d find an energy measured in units of slugs cubit[sup]2[/sup]/fortnight[sup]2[/sup], which is a perfectly valid unit of energy (even if it’s never actually used by anyone). The convenience of using one of the metric systems is that if you get energy in kilograms meter[sup]2[/sup]/second[sup]2[/sup] (or in grams centimeter[sup]2[/sup]/second[sup]2[/sup], there’s a short, convenient name for that unit (Joule or erg, respectively). ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [October 22, 2003, 4:31pm UTC](https://boards.straightdope.com/t/e-mc-2-applied/208638/23 "2003-10-22T16:31:28Z")
Oops, if I really had been careful I wouldn’t of said mass-energy I would of said **rest energy**. The equation E = mc[sup]2[/sup] is called the mass-energy equation. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [October 22, 2003, 8:02pm UTC](https://boards.straightdope.com/t/e-mc-2-applied/208638/24 "2003-10-22T20:02:39Z")
> [@](#): > > \*Originally posted by MC Master of Ceremonies \* > \*\*Oops, if I really had been careful I wouldn’t of said mass-energy I would of said **rest energy**. The equation E = mc[sup]2[/sup] is called the mass-energy equation. \*\* True, but in general you can’t say that the mass of a system is equal to E/c[sup]2[/sup]. That’s only valid in the system’s rest frame. The equation that holds for all frames is m = (E[sup]2[/sup]/c[sup]4[/sup] - p[sup]2[/sup]/c[sup]2[/sup])[sup]1/2[/sup] It is also not really correct to say that mass is converted to energy since the mass of the system does not change. ---
**Author:** ![robo99](https://avatars.discourse-cdn.com/v4/letter/r/a8b319/32.png) [@robo99](https://boards.straightdope.com/u/robo99)\ **Post date:** [October 23, 2003, 4:40am UTC](https://boards.straightdope.com/t/e-mc-2-applied/208638/25 "2003-10-23T04:40:16Z")
Sorry to but in, I just wanted to bring up something that irks me about \c\ that easily confuses people who are trying to learn this stuff for the first time. \c\ is NOT the speed of light. \c\ is the speed of light in a vacuum. This should be repeated as a mantra by all newbies. ---
**Author:** ![robo99](https://avatars.discourse-cdn.com/v4/letter/r/a8b319/32.png) [@robo99](https://boards.straightdope.com/u/robo99)\ **Post date:** [October 23, 2003, 4:44am UTC](https://boards.straightdope.com/t/e-mc-2-applied/208638/26 "2003-10-23T04:44:22Z")
Sorry about that - not allowed to edit my posts - how do you do bold in this forum? ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [October 23, 2003, 4:57am UTC](https://boards.straightdope.com/t/e-mc-2-applied/208638/27 "2003-10-23T04:57:19Z")
> [@](#): > > \*Originally posted by robo99 \* > \*\*Sorry about that - not allowed to edit my posts - how do you do bold in this forum? \*\* Square brackets, not angle brackets. For more info on coding, click down below where it says “vB code is On”. I agree **c** shouldn’t be called “speed of light.” Every time someone says “you can’t go faster than the speed of light” I’m tempted to say “sure you can, what do you think Cherenkov radiation is?” The Einstein Constant is a better name. [Previous page](https://boards.straightdope.com/t/e-mc-2-applied/208638.md?page=1)