4 ms·

I'm fairly certain a square manhole cover with a sufficient perimeter would still have no chance of falling into a hole, depending on the diameter of said hole.

beached_whale 5y ago
If you provide a sufficient lip on the hole such that the minimum side is larger than any of the four diagonals it would work.
- kragen 5y ago
  Right, but this makes the area of the cover twice the area of the hole, and the cover twice as heavy as it would need to be if it were round. As Feynman pointed out, even round covers are already pretty heavy—I injured my wrist (ligaments?) from the tension of lifting one in my teens. However, if this were the only consideration, you could get a wider-diameter manhole with a smaller cover by making it in the form of an equilateral triangle, as evidently Nashua, NH, does: https://en.wikipedia.org/wiki/Manhole_cover#Other https://en.wikipedia.org/wiki/Manhole_cover#Other. Indeed, you don't need to stop there; if you curve the sides of the triangle in toward the center, you can get a manhole with an even smaller surface area for a given diameter, although at some point the extra "diameter" will be too curved to be useful.
- MathYouF 5y ago
  Indeed, though to do it this way would be very wasteful of resources as the ratio of the manhole size to the size of the cover wouldn't be maximized. The cover would be needlessly covering a lip whose large size only exists because of the poor choice of shape.
  - deleted 5y ago
    [deleted]
zucker42 5y ago
It explains in the joke how it's possible to fit a square cover into a slightly smaller square hole. The easiest way is to position the cover vertically and across the diagonal. The lip that the square cover rests on would have to be impractically large to fully prevent the cover from fitting into the hole.
rdiddly 5y ago
If we're talking square cover, round hole, no cover big enough to cover the hole could fall in.
ryandvm 5y ago
If I know anything about capitalism, the primary reason manhole covers are round is because that's the most cost-efficient shape for the job.
- nonameiguess 5y ago
  This is almost certainly the answer. They're round to fit the cylindrical holes they're covering, and those holes are round because they're made with drills, and they're made with drills because that's a lot faster and cheaper than digging.
  - yobbo 5y ago
    Tunnels are round because a round tube on the inside is stronger against compression than an equivalent square tube is. They are like vaults.

beached_whale 5y ago

If you provide a sufficient lip on the hole such that the minimum side is larger than any of the four diagonals it would work.

kragen 5y ago
Right, but this makes the area of the cover twice the area of the hole, and the cover twice as heavy as it would need to be if it were round. As Feynman pointed out, even round covers are already pretty heavy—I injured my wrist (ligaments?) from the tension of lifting one in my teens. However, if this were the only consideration, you could get a wider-diameter manhole with a smaller cover by making it in the form of an equilateral triangle, as evidently Nashua, NH, does: https://en.wikipedia.org/wiki/Manhole_cover#Other https://en.wikipedia.org/wiki/Manhole_cover#Other. Indeed, you don't need to stop there; if you curve the sides of the triangle in toward the center, you can get a manhole with an even smaller surface area for a given diameter, although at some point the extra "diameter" will be too curved to be useful.
MathYouF 5y ago
Indeed, though to do it this way would be very wasteful of resources as the ratio of the manhole size to the size of the cover wouldn't be maximized. The cover would be needlessly covering a lip whose large size only exists because of the poor choice of shape.
- deleted 5y ago
  [deleted]

zucker42 5y ago

It explains in the joke how it's possible to fit a square cover into a slightly smaller square hole. The easiest way is to position the cover vertically and across the diagonal. The lip that the square cover rests on would have to be impractically large to fully prevent the cover from fitting into the hole.

rdiddly 5y ago

If we're talking square cover, round hole, no cover big enough to cover the hole could fall in.

ryandvm 5y ago

If I know anything about capitalism, the primary reason manhole covers are round is because that's the most cost-efficient shape for the job.

nonameiguess 5y ago
This is almost certainly the answer. They're round to fit the cylindrical holes they're covering, and those holes are round because they're made with drills, and they're made with drills because that's a lot faster and cheaper than digging.
- yobbo 5y ago
  Tunnels are round because a round tube on the inside is stronger against compression than an equivalent square tube is. They are like vaults.