# Physics Vocab Query **URL:** \ **Category:** Factual Questions\ **Created:** [June 30, 2002, 5:37am UTC](https://boards.straightdope.com/t/physics-vocab-query/116669 "2002-06-30T05:37:45Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Qwertyasdfg](https://avatars.discourse-cdn.com/v4/letter/q/ecc23a/32.png) [@Qwertyasdfg](https://boards.straightdope.com/u/Qwertyasdfg)\ **Post date:** [June 30, 2002, 5:37am UTC](https://boards.straightdope.com/t/physics-vocab-query/116669/1 "2002-06-30T05:37:45Z")
If mass and energy are different manifestations of the same thing (E = mc^2), what is the larger group that they are both subsets of called? ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [June 30, 2002, 6:47am UTC](https://boards.straightdope.com/t/physics-vocab-query/116669/2 "2002-06-30T06:47:57Z")
I believe momentum and inertia also fit in with those two. I would guess that they are subsets of mass. (So I guess mass wouldn’t be included in the list). But I’m just taking a guess. ---
**Author:** ![John\_Kentzel-Griffin](https://avatars.discourse-cdn.com/v4/letter/j/ccd318/32.png) [@John\_Kentzel-Griffin](https://boards.straightdope.com/u/John_Kentzel-Griffin)\ **Post date:** [June 30, 2002, 6:54am UTC](https://boards.straightdope.com/t/physics-vocab-query/116669/3 "2002-06-30T06:54:43Z")
Mass-energy. ---
**Author:** ![John\_Kentzel-Griffin](https://avatars.discourse-cdn.com/v4/letter/j/ccd318/32.png) [@John\_Kentzel-Griffin](https://boards.straightdope.com/u/John_Kentzel-Griffin)\ **Post date:** [June 30, 2002, 7:00am UTC](https://boards.straightdope.com/t/physics-vocab-query/116669/4 "2002-06-30T07:00:04Z")
The amount of inertia is the amount of mass. Momentum is approx mass time velocity for small velocities. ---
**Author:** ![JS\_Princeton](https://avatars.discourse-cdn.com/v4/letter/j/57b2e6/32.png) [@JS\_Princeton](https://boards.straightdope.com/u/JS_Princeton)\ **Post date:** [June 30, 2002, 7:52pm UTC](https://boards.straightdope.com/t/physics-vocab-query/116669/5 "2002-06-30T19:52:12Z")
momentum is an operator. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [July 1, 2002, 5:09pm UTC](https://boards.straightdope.com/t/physics-vocab-query/116669/6 "2002-07-01T17:09:13Z")
> [@](#): > > If mass and energy are different manifestations of the same thing (E = mc^2), what is the larger group that they are both subsets of called? Energy and mass aren’t really the same thing: M[sup]2[/sup]C[sup]4[/sup] = E[sup]2[/sup] - P[sup]2[/sup]C[sup]2[/sup] (or, with C==1, M[sup]2[/sup] = E[sup]2[/sup] - P[sup]2[/sup]) where P is momentum. A question anlogous to the OP would be to ask, “Since speed and velocity are different manifestations of the same thing, what is the larger group that speed and velocity are subsets of?”. I’m not sure that this has a satisfying answer. > [@](#): > > Mass-energy. Is this an accepted physics term? I thought it your own invention. ---
**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:** [July 1, 2002, 9:24pm UTC](https://boards.straightdope.com/t/physics-vocab-query/116669/7 "2002-07-01T21:24:33Z")
In actual usage in relativity, “energy” is usually used as the generic term, and can roughly be broken down into “mass” and “kinetic energy”. Yes, there’s potential energy, but that’s actually part of “mass”, and thermal energy is part of “kinetic”. Outside of relativity, the terminology is different, but then, outside of relativity, you’re not usually worrying about E = mc[sup]2[/sup].