this post was submitted on 22 May 2024
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xkcd #2935: Ocean Loop (imgs.xkcd.com)
submitted 5 months ago by [email protected] to c/[email protected]
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https://xkcd.com/2935

Alt text:

I can't believe they wouldn't even let me hold a vote among the passengers about whether to try the loop.

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[–] [email protected] 12 points 5 months ago* (last edited 5 months ago) (4 children)

How fast would the water have to be traveling for this to actually work? Pretty sure there was a waterslide built with a loop once and it infamously didn't work, but those work on gravity alone. With enough pressure it should be able to loop, right? Or would it just get wonky because it's a fluid? πŸ€”

I feel like this could be one of those things that works perfectly if you make a small model, but won't ever scale up due to reasons.

[–] [email protected] 2 points 5 months ago

Could you get 3 cats to do what you want? Maybe. What about 300 million cats? Water is like a cat sometimes lol

  • my self taught fluid dynamics knowledge AKA fuck fluid dynamics
[–] [email protected] 4 points 5 months ago

I feel like it'd need to go at super sonic speed.

[–] [email protected] 8 points 5 months ago (1 children)

I don't think he's done one with ocean liners but he did one with trains.

[–] [email protected] 3 points 5 months ago

I was actually more curious about the water itself and forgot we were even talking about a boat lol. Could you force that much through an open loop without it sloshing back inward?

[–] [email protected] 9 points 5 months ago (2 children)

Holy shit I wonder if it's even humanly possible to build one of these in the ocean for any size ship.

[–] [email protected] 4 points 5 months ago (1 children)

You just have to go fast enough. The minimum speed keeping you from falling out of a circular loop is sqrt(gr), with gravitational acceleration g and loop radius r. 10m radius requires 36km/h, which might be suitable for a Jetski. Larger ships need bigger loops to physically fit, and consequently larger speeds. It's quite surprising, but a monstrous 100m radius loop needs less than 120km/h.

[–] [email protected] 1 points 5 months ago (1 children)

so mass doesn't factor into the equation??? a Jetski made from aluminum would need the same speed as from osmium?

[–] [email protected] 1 points 5 months ago

I think so. At the apex of the loop gravity balances centrifugal force, Fg = Fc, when going the minimal speed necessary to get through the loop. Fg = m g, Fc = m v^2 / r. So mass m drops out of the equation.

[–] [email protected] 7 points 5 months ago (2 children)

Maybe something small, like a jetski…

[–] [email protected] 4 points 5 months ago (1 children)

How about a duck

[–] [email protected] 4 points 5 months ago

Or a witch.

[–] [email protected] 5 points 5 months ago (1 children)

Cruise ship or bust.

And it's just a drawing but I'm trying to realize it in actual size. Cruise ships are huge, pushing 250 or so feet out of the water. That's considered a high-rise in the construction world.

Now I look at that loopdy-lopp and say hey, that boat could fit. I'm ignoring all the other physics and shit and just Matchbox car'g that boat through that loop. That makes that loop like, what, 1000 feet? And that is ignoring the structure beneath the surface, and also the other dimensions of this, and the sheer velocity and volume of water.

So I'm gonna call this one a hard maybe. Perhaps if the world could set aside it's differences, we could do a sort of space race, but instead a ship flip, or a boat float, or some other rhyme.

[–] [email protected] 5 points 5 months ago

sounds like an idea for a "what if" scenario. I know just the author to pitch this to...

[–] [email protected] 7 points 5 months ago (1 children)

Maybe they're just on the Grand Line headed to the new world?

[–] [email protected] 5 points 5 months ago

With enough knock up power maybe we could reach the sky with this bad boy.

[–] [email protected] 16 points 5 months ago (1 children)

Tales from the Loop

Sorrynotsorry, I've just got into watching it and it fit so... haha.

[–] [email protected] 4 points 5 months ago

Thanks, you just gave me something to watch :-)

(Although I'll finish my current season of doctor who first)

[–] [email protected] 55 points 5 months ago (1 children)

Next try to calculate what it would actually mean to make that much water follow a path like that. My guess is, it’s going to get very spicy.

[–] [email protected] 56 points 5 months ago (1 children)

The xkcd explained brushes near it.

Many of the passengers would suffer extreme injuries from the changes of velocity (up to 230 mph based on a loop radius of 3 x ship length) and rotation (unlike rollercoasters, or even airplanes during simple take-off and landing, passengers aren't normally strapped down).

[–] [email protected] 9 points 5 months ago

Can't you just tell them to hold on to something?

[–] [email protected] 21 points 5 months ago

https://explainxkcd.com/2935