# Equal and Opposite Forces?

**URL:** <https://boards.straightdope.com/t/equal-and-opposite-forces/358658>\
**Category:** Factual Questions\
**Created:** [May 29, 2006, 8:48pm UTC](https://boards.straightdope.com/t/equal-and-opposite-forces/358658 "2006-05-29T20:48:12Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\
**Post date:** [May 31, 2006, 12:41am UTC](https://boards.straightdope.com/t/equal-and-opposite-forces/358658/21 "2006-05-31T00:41:31Z")

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> [@Mathochist](#):
>
> It wouldn’t be like much of anything at all, since special relativity wouldn’t be in effect, taking quantum field theory and general relativity out with it, and pretty much nothing would work. Electrons would spiral into nuclei and everything would annihilate into energy, which would cool down right quick what with the universe expanding infinitely fast and taking radiation along with it.

So I guess we need a “Don’t walk here” sign, eh?

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**Author:** ![SandyHook](https://avatars.discourse-cdn.com/v4/letter/s/dec6dc/32.png) [@SandyHook](https://boards.straightdope.com/u/SandyHook)\
**Post date:** [May 31, 2006, 12:50am UTC](https://boards.straightdope.com/t/equal-and-opposite-forces/358658/22 "2006-05-31T00:50:17Z")

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> [@BACI](#):
>
> Years ago, I was told that the reason why you don’t sink into the ground when you walk is that the surface you’re walking on applies an equal but opposite force on your foot where you are standing. ie If my foot carries **80kg of force as I step forward, the ground under my foot applies an 80kg force back.**  
> M

Shouldn’t that be 80 fig newtons, or something?

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**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\
**Post date:** [May 31, 2006, 1:07am UTC](https://boards.straightdope.com/t/equal-and-opposite-forces/358658/23 "2006-05-31T01:07:49Z")

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> [@Mathochist](#):
>
> > [@ultrafilter](#):
> >
> > That raises another question: what would it be like to walk on an infinitely rigid surface?
> 
> It wouldn’t be like much of anything at all, since special relativity wouldn’t be in effect, taking quantum field theory and general relativity out with it, and pretty much nothing would work. Electrons would spiral into nuclei and everything would annihilate into energy, which would cool down right quick what with the universe expanding infinitely fast and taking radiation along with it.

Ah, but what would it be like to walk around an infinitely long rotating cylinder?

Stranger

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