# What do the units of energy measurement mean in E=mc^2?

**URL:** <https://boards.straightdope.com/t/what-do-the-units-of-energy-measurement-mean-in-e-mc-2/685104>\
**Category:** Factual Questions\
**Created:** [April 1, 2014, 6:11pm UTC](https://boards.straightdope.com/t/what-do-the-units-of-energy-measurement-mean-in-e-mc-2/685104 "2014-04-01T18:11:54Z")\
**Posts on this page:** 4\
**Page:** 4

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**Author:** ![filmore](https://avatars.discourse-cdn.com/v4/letter/f/7993a0/32.png) [@filmore](https://boards.straightdope.com/u/filmore)\
**Post date:** [April 6, 2014, 1:11am UTC](https://boards.straightdope.com/t/what-do-the-units-of-energy-measurement-mean-in-e-mc-2/685104/61 "2014-04-06T01:11:35Z")

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> [@lawbuff](#):
>
> Oh add, Filmore, the OP has not come back to tell that I am misunderstanding it, if he did HE could explain it better, you are interpreting it for him. Brightsunny was a smart aleck in post 8 anyway, soooo…
> 
> I have no further need in this thread to fight with him or you.

To be honest, I’m confused about what you’re trying to argue. I didn’t say anything because I wasn’t sure if you were discussing a more advanced concept that was over my head.

I do understand that it is :

(mass) x (meter)^2 / (seconds)^2

and not:

(mass x meter / seconds )^ 2

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**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\
**Post date:** [April 6, 2014, 4:43am UTC](https://boards.straightdope.com/t/what-do-the-units-of-energy-measurement-mean-in-e-mc-2/685104/62 "2014-04-06T04:43:50Z")

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Hey, OP, stay out of this.  
🙂

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**Author:** ![BrightNShiny](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@BrightNShiny](https://boards.straightdope.com/u/BrightNShiny)\
**Post date:** [April 6, 2014, 5:25am UTC](https://boards.straightdope.com/t/what-do-the-units-of-energy-measurement-mean-in-e-mc-2/685104/63 "2014-04-06T05:25:56Z")

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> [@filmore](#):
>
> To be honest, I’m confused about what you’re trying to argue. I didn’t say anything because I wasn’t sure if you were discussing a more advanced concept that was over my head.
> 
> I do understand that it is :
> 
> (mass) x (meter)^2 / (seconds)^2
> 
> and not:
> 
> (mass x meter / seconds )^ 2

You’re doing fine. **lawbuff** is posting confused responses. The other posters in this thread have useful information, so you should focus on that.

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**Author:** ![UTejas](https://avatars.discourse-cdn.com/v4/letter/u/977dab/32.png) [@UTejas](https://boards.straightdope.com/u/UTejas)\
**Post date:** [April 6, 2014, 5:43am UTC](https://boards.straightdope.com/t/what-do-the-units-of-energy-measurement-mean-in-e-mc-2/685104/64 "2014-04-06T05:43:07Z")

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OP, this type of problem that you are describing falls under the general term “dimensional analysis.” The [wikipedia article](http://en.wikipedia.org/wiki/Dimensional_analysis) is pretty good. The general idea is that there are only a few fundamental units that need to be defined–distance, time, mass, electric charge, and a couple others. All other quantities and units are all then defined in terms of those fundamental quantities. For instance, velocity is defined in terms of length / time.

Dimensional analysis deals with understanding how to compare these quantities to one another and whether that comparison is fair. The wikipedia section on commensurability is particularly useful in this context. Dimensional analysis lets you figure out that, for example, adding a kilogram to an hour has no meaning, but dividing a kilogram by an hour can represent a change in mass over time.

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