4 ms·

> ...floating forms that nest neatly in the rounded curves of modern devices. These clearly defined shapes feel easy to tap and are designed to relate to the na

by cyode 1y ago

> ...floating forms that nest neatly in the rounded curves of modern devices. These clearly defined shapes feel easy to tap and are designed to relate to the natural geometry of our fingers... This reminds me for some reason of my preferred answer to the Microsoft interview question "Why are manholes round?" A: Because the average cross-section of a human being is roughly circular.

deaddodo 1y ago
That answer would be akin to someone asking “why is the sun round?” and answering with “it’s roughly the optimal shape for viewing the totality of the sun”.
dylan604 1y ago
Is that the real reason? I had always heard that a round hole prevents the cover from being able to fall back in the hole
- derefr 1y ago
  From the perspective of "design the manhole cover first", the reason is that manhole covers aren't just round — they're (very subtle) domes. A dome is: 1. the best shape for taking stress from very heavy trucks putting all their weight on them without the manhole itself gradually bowing, and 2. is best at transferring that stress equally into the manhole wall (cast concrete cylinder) itself. (A square manhole + manhole cover would disperse force unfairly, potentially gradually cracking the manhole walls / requiring stronger walls. A flat circular manhole would disperse force upon the center of the manhole equally onto the manhole walls, allowing for lower-material-cost manhole walls. A domed manhole cover additionally disperses force from most points on the dome equally into the manhole walls — important, as vehicles won't necessarily be driving over the exact center of the manhole!) ...but really, this is the wrong direction to work in. The original reason manhole covers are round, is simply that the walls of a manhole are best made round, for the same reason drink cans and barrels are best made round: a closed cylinder is great at taking compressive force from a lid above; passing it through as soft, equal tensile force through its walls without buckling strain; and then turning that force back into an equal compressive force on the floor / subsurface. Most manholes are generally small closed cylinders acting as maintenance areas for nearby pipes, with the pipes coming in through the sides of the manhole walls, and the concrete bottom floor of the manhole resting upon compacted earth. In this situation, any shape for the manhole other than a cylinder — if driven over for years/decades by cars — would gradually pound the uneven force acting upon the manhole's floor into the earth below, unevenly accelerating soil subsidence. Eventually, you've created a sinkhole below the road, right outside the manhole wall on one side.
  - adastra22 1y ago
    As someone with a mechanical engineering background, all these clever answers to the question (e.g. "manhole covers are round to prevent the cover falling in") are strange. Covers are round because the hole is round, and the hole is round because a cylindrical shape is sturdy and prevents collapse. That's it.
    - nomel 1y ago
      That's not "it". A square cover would not be feasible, without a tether system to fish them out of the literal shit, after they fall in from a few inch misalignment.
      - adastra22 1y ago
        Why would you put a square cover on a round hole? The hole came first. They dig a hole, then they have a need to put a cover on it. Making a circular cover to fit over a circular hole is if anything cheaper and easier than making a square cover over an inscribed circular hole, at least when working with metal. The hole drove the design of the cover, not the other way around.
        derefr 1y ago
        In this hypothetical, presuming you're putting the manhole (subsurface conduit/plumbing maintenance access point) in after you've already paved the road: it's because the tool you'd use to cut a hole into pavement (i.e. a concrete saw) cuts straight lines — and it's easier to make a square/rectangle out of straight lines than a circle. And sure enough, whenever you see workers hacking up the road, they generally are cutting square holes. Refer, after that, to the process of constructing a manhole (https://www.envirodesignproducts.com/blogs/news/how-are-manholes-made https://www.envirodesignproducts.com/blogs/news/how-are-manh...). At the end of this process, you have a square hole in the pavement, opening to a square excavation, bottoming out at a square concrete foundation, on which has been set a round concrete cylinder, which is then surrounded out to the edge of the square hole with packed earth. Given this, you could equally-well finish this job either: 1. by placing a square of metal to fill the entire square packed-earth space you've constructed (as when bridging a pothole with a temporary steel surface plate); 2. or by first paving over the exposed packed-earth part, and then placing a circle of metal to cover only the manhole entrance itself. ...which is why people do justifiably ask why, in practice, we seem to always favor option 2 over option 1.
- seanhunter 1y ago
  If that was the reason a Reuleaux triangle would have the same property while using (I think) less material for a given size of shaft (as long as the shaft can be triangular). https://en.wikipedia.org/wiki/Reuleaux_triangle https://en.wikipedia.org/wiki/Reuleaux_triangle
  - seanhunter 1y ago
    To explain myself better now I am awake and have had coffee: What makes a cover that cannot fall down the hole that it is covering? The width[1] of the closed curve has to be larger than that of the hole. A circle is easy to understand because it is a closed curve of fixed width, but a Reuleaux triangle is also a closed curve of fixed width, meaning if that fixed width is greater than the widest part of the hole, then there is no orientation of the cover in 3D that will allow it to fall down the hole. It’s easy to see if you take an equilateral triangle, circumscribe it with the smallest circle and then (mentally) construct the Reuleaux triangle that the Reuleaux triangle sits inside the circle and so would use less material. [1] This is defined as the minimum perpendicular distance between parallel lines bounding the shape.
- Groxx 1y ago
  It's cheap and easy to install a vertical pipe when you're already laying a ton of horizontal pipe.
nofunsir 1y ago
I prefer the Feynman approach to answering Why questions... until they throw me out.
seanhunter 1y ago
Most manhole covers aren’t round. If you actually go out and look at them, the vast majority of manhole covers are rectangular.
- v5v3 1y ago
  Are you talking globally or just USA?
  - seanhunter 1y ago
    I guess it varies by country which I should have acknowledged. I was talking UK and EU and Africa which I am most familiar with, although I have also been to the USA and Asia and seen manhole covers there. You certainly get round manhole covers, but there are far more rectangular ones. Eg this kind of thing https://www.drainageshop.co.uk/polydrain-inspection-chamber/320mm-diameter-square-pp-manhole-cover-frame-a15-pedestrian-duty.html https://www.drainageshop.co.uk/polydrain-inspection-chamber/...
- Andrew_nenakhov 1y ago
  I don't think I've ever seen non-round manhole cover. In all exUSSR countries they are round.
ErrorNoBrain 1y ago
But the real answer is, that it prevents the cover from falling in... it's a safety feature :(

by cyode 1y ago

deaddodo 1y ago

That answer would be akin to someone asking “why is the sun round?” and answering with “it’s roughly the optimal shape for viewing the totality of the sun”.

dylan604 1y ago

Is that the real reason? I had always heard that a round hole prevents the cover from being able to fall back in the hole

derefr 1y ago
From the perspective of "design the manhole cover first", the reason is that manhole covers aren't just round — they're (very subtle) domes. A dome is: 1. the best shape for taking stress from very heavy trucks putting all their weight on them without the manhole itself gradually bowing, and 2. is best at transferring that stress equally into the manhole wall (cast concrete cylinder) itself. (A square manhole + manhole cover would disperse force unfairly, potentially gradually cracking the manhole walls / requiring stronger walls. A flat circular manhole would disperse force upon the center of the manhole equally onto the manhole walls, allowing for lower-material-cost manhole walls. A domed manhole cover additionally disperses force from most points on the dome equally into the manhole walls — important, as vehicles won't necessarily be driving over the exact center of the manhole!) ...but really, this is the wrong direction to work in. The original reason manhole covers are round, is simply that the walls of a manhole are best made round, for the same reason drink cans and barrels are best made round: a closed cylinder is great at taking compressive force from a lid above; passing it through as soft, equal tensile force through its walls without buckling strain; and then turning that force back into an equal compressive force on the floor / subsurface. Most manholes are generally small closed cylinders acting as maintenance areas for nearby pipes, with the pipes coming in through the sides of the manhole walls, and the concrete bottom floor of the manhole resting upon compacted earth. In this situation, any shape for the manhole other than a cylinder — if driven over for years/decades by cars — would gradually pound the uneven force acting upon the manhole's floor into the earth below, unevenly accelerating soil subsidence. Eventually, you've created a sinkhole below the road, right outside the manhole wall on one side.
- adastra22 1y ago
  As someone with a mechanical engineering background, all these clever answers to the question (e.g. "manhole covers are round to prevent the cover falling in") are strange. Covers are round because the hole is round, and the hole is round because a cylindrical shape is sturdy and prevents collapse. That's it.
  - nomel 1y ago
    That's not "it". A square cover would not be feasible, without a tether system to fish them out of the literal shit, after they fall in from a few inch misalignment.
    - adastra22 1y ago
      Why would you put a square cover on a round hole? The hole came first. They dig a hole, then they have a need to put a cover on it. Making a circular cover to fit over a circular hole is if anything cheaper and easier than making a square cover over an inscribed circular hole, at least when working with metal. The hole drove the design of the cover, not the other way around.
      - derefr 1y ago
        In this hypothetical, presuming you're putting the manhole (subsurface conduit/plumbing maintenance access point) in after you've already paved the road: it's because the tool you'd use to cut a hole into pavement (i.e. a concrete saw) cuts straight lines — and it's easier to make a square/rectangle out of straight lines than a circle. And sure enough, whenever you see workers hacking up the road, they generally are cutting square holes. Refer, after that, to the process of constructing a manhole (https://www.envirodesignproducts.com/blogs/news/how-are-manholes-made https://www.envirodesignproducts.com/blogs/news/how-are-manh...). At the end of this process, you have a square hole in the pavement, opening to a square excavation, bottoming out at a square concrete foundation, on which has been set a round concrete cylinder, which is then surrounded out to the edge of the square hole with packed earth. Given this, you could equally-well finish this job either: 1. by placing a square of metal to fill the entire square packed-earth space you've constructed (as when bridging a pothole with a temporary steel surface plate); 2. or by first paving over the exposed packed-earth part, and then placing a circle of metal to cover only the manhole entrance itself. ...which is why people do justifiably ask why, in practice, we seem to always favor option 2 over option 1.
seanhunter 1y ago
If that was the reason a Reuleaux triangle would have the same property while using (I think) less material for a given size of shaft (as long as the shaft can be triangular). https://en.wikipedia.org/wiki/Reuleaux_triangle https://en.wikipedia.org/wiki/Reuleaux_triangle
- seanhunter 1y ago
  To explain myself better now I am awake and have had coffee: What makes a cover that cannot fall down the hole that it is covering? The width[1] of the closed curve has to be larger than that of the hole. A circle is easy to understand because it is a closed curve of fixed width, but a Reuleaux triangle is also a closed curve of fixed width, meaning if that fixed width is greater than the widest part of the hole, then there is no orientation of the cover in 3D that will allow it to fall down the hole. It’s easy to see if you take an equilateral triangle, circumscribe it with the smallest circle and then (mentally) construct the Reuleaux triangle that the Reuleaux triangle sits inside the circle and so would use less material. [1] This is defined as the minimum perpendicular distance between parallel lines bounding the shape.
Groxx 1y ago
It's cheap and easy to install a vertical pipe when you're already laying a ton of horizontal pipe.

nofunsir 1y ago

I prefer the Feynman approach to answering Why questions... until they throw me out.

seanhunter 1y ago

Most manhole covers aren’t round. If you actually go out and look at them, the vast majority of manhole covers are rectangular.

v5v3 1y ago
Are you talking globally or just USA?
- seanhunter 1y ago
  I guess it varies by country which I should have acknowledged. I was talking UK and EU and Africa which I am most familiar with, although I have also been to the USA and Asia and seen manhole covers there. You certainly get round manhole covers, but there are far more rectangular ones. Eg this kind of thing https://www.drainageshop.co.uk/polydrain-inspection-chamber/320mm-diameter-square-pp-manhole-cover-frame-a15-pedestrian-duty.html https://www.drainageshop.co.uk/polydrain-inspection-chamber/...
Andrew_nenakhov 1y ago
I don't think I've ever seen non-round manhole cover. In all exUSSR countries they are round.

ErrorNoBrain 1y ago

But the real answer is, that it prevents the cover from falling in... it's a safety feature :(