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xkcd #2935: Ocean Loop
(imgs.xkcd.com)
Alt text:
I can't believe they wouldn't even let me hold a vote among the passengers about whether to try the loop.
Holy shit I wonder if it's even humanly possible to build one of these in the ocean for any size ship.
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.
so mass doesn't factor into the equation??? a Jetski made from aluminum would need the same speed as from osmium?
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.