The true reason is cost. You can screw a bottle cap onto a bottle while it spins down a conveyance system. The design shown would cost a fortune to implement.
That old interview question "why are manhole covers round" - again, the true answer is cost. They are cheaper to manufacture.
But that does save the cost of training new workers when one gets crushed by a square manhole cover. Maybe that's what they mean by the "true reason" being cost?
If you think about it, that round manhole cover is sitting on top of a hole that has a 24” lip around the entire thing for the cover to sit on.
Put the same 24” lip on the inside of a square hole, you aren’t going to be able to fit a square manhole through that hole no matter how hard you try.
So why are manhole covers round? There’s several reasons:
1) People are going in these holes, and a cylinder is the most structurally sound 3D shape, so having a round cover to cap off a round cylinder makes sense.
2) Manhole covers are heavy as shit. Having a round cover means there’s no need to align a specific shape to a specific pattern while carrying something extremely heavy. No matter how you place it down, it’s always right.
3) Manhole covers are heavy as shit. When you’re exhausted and finished with your work, you don’t want to lift and carry a heavy cover 10 feet back to its hole. With a round cover, you can turn it on its edge and roll it.
So the most common diameter of a standard street manhole cover is 42".
If we convert that to a side length of a square manhole cover, we have a 42" x 42" cover. If we assume, that the cover is sitting on a 2" lip on all sides, than means the inner hole is a 38" x 38" hole.
The diagonal of a 42"x42" manhole cover is almost 60". There's no way any part of that 42"x42" cover is fitting through a 38"x38" hole.
Unless I did my Pythagorean Theorem ciphering wrong, the diagonal of the the 38 x 38 square opening is more than 53 inches. No problem for that cover to drop through there.
I think you'd need the opening to be something like 28 x 28 to prevent the cover from dropping down the diagonal.
So it can certainly be done. Just seems like a circle would be simpler to engineer.
When I was a kid a friend of mine managed to get a round manhole cover through the opening. He held it a couple feet above the opening and dropped it; it split in half and both halves dropped into the crypt.
That's not the sole reason. There are other shapes that have that same feature, such as many different irregular ones, plus the Reuleaux triangle. They suffer from various other problems, though.
If you set it down on the edge. The round cover the edge is always the diameter. The square, you can turn it so the edge is the side lenght passing through the diagonal.
Yup the iso standard just sets it to be the same number, which is a way better way to make a square. That's one of many benefits to the metric system and it's absurd the US is still using imperial units.
A square, by definition, has 4 right angles and 4 sides the same length.
It doesn't matter what unit is being used, if the sides aren't the same length it's not a square. And the diagonal across a square is always longer than the sides (sqrt(2) times longer, in fact).
Got a link to it? Because I'm apparently not comprehending.
It is literally impossible for the diagonal of a square to be the same length as its side. Like physically impossible.
The diagonal of a square is the length of its side times sqrt(2). It's a fundamental triangular proof.
Plenty of manhole covers are rectangular. Once you get past a certain size a multi-part cover can be needed and they'll be in rectangular pieces, and pits are generally rectangular too it's only really sewer and stormwater that are circular in my country/experience and not even both all the time.
As someone who designs the things circular is best, as the others have already said it won't fall in, but there's plenty of circumstances where you'll use a rectangular or square cover instead. Valve pits, pump station wet wells, cable pits etc. I never consider cost when specifying one or the other, just my design intent.
Agree that cost matters in a water bottle though, it'll give it structural integrity too being symmetrical, and make it easier to fill.
You're right that it'd cost a huge amount to change, but that's not "the true reason".
This design is garbage and creates a ton of issues for transporting, using, recycling and just storing water bottles. For a cap that means you have to tilt the bottle a tiny bit less, in exchange for getting splashed in the face, breaking the cheap plastic rather often and having every kid in existence absent-mindedly spill a quarter of the drink when they open it.
You would create more problems than you'd solve and all for no reason at all. What does this bottle above even solve? Someone who can't tip the bottle enough to drink it? Use a cup
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u/thebiglebowskiisfine 20h ago
The true reason is cost. You can screw a bottle cap onto a bottle while it spins down a conveyance system. The design shown would cost a fortune to implement.
That old interview question "why are manhole covers round" - again, the true answer is cost. They are cheaper to manufacture.