this post was submitted on 23 Oct 2024
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Cyberpunk 2077

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[–] ObviouslyNotBanana@lemmy.world 129 points 3 weeks ago* (last edited 3 weeks ago) (12 children)

I have never thought about the fact that manhole covers need to hold up to weight. Of course they do and it's perfectly normal and sensible. It's just not a thought I've ever had.

[–] 9point6@lemmy.world 79 points 3 weeks ago (9 children)

Technically it's the manhole covers that need to support the weight.

Manholes themselves are expected to do the opposite of holding weight

[–] usualsuspect191@lemmy.ca 46 points 3 weeks ago (7 children)

Manholes themselves are expected to do the opposite of holding weight

They hold light?

[–] WldFyre@lemm.ee 8 points 3 weeks ago (2 children)

Structures underground experience buoyant forces that act to push them up. Manholes (and any structure bottom, like storm inlets, pump station wet wells, etc) need special consideration since they can be partially or mostly hollow, so they have to be heavy enough to remain in place.

[–] usualsuspect191@lemmy.ca 5 points 3 weeks ago (1 children)

You know, I knew that but couldn't figure out what the opposite of weight was for some reason. Thanks for the extra learning!

Fun fact: Coffins experience this force too, and during flooding can rise up out of the ground

[–] superkret@feddit.org 2 points 3 weeks ago* (last edited 3 weeks ago)

Ah, that explains why my grandpa was buried in a lead coffin.
He lost a lot of weight right before he died, so he was too light!

[–] bnaur@lemmy.world 2 points 3 weeks ago* (last edited 3 weeks ago) (1 children)

Right, so the light is actually pushed up by these buoyant forces and I guess that then also explains why it's so dark underground. Fascinating how learning some little new details about the world can sometimes make it all just click together!

But does that mean that light is actually hollow?

[–] Enkrod@feddit.org 2 points 3 weeks ago

Well we know light is concentrated into comparatively tiny, but heavy points in the universe (stars), while dark fills the vast vacuum of space. So light in itself is likely denser than dark, ergo the light we have on earth must be forming hollow structures to remain lighter than dark when comparing by volume.

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