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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.
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.