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Old May 2nd 2014, 02:30 AM   #1
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Unknown Phenomenon

Hey guys, i have a presentation to do on a chosen topic that relates in some way to fluid mechanics. I have chosen mine to be based on whitewater kayaking since im enthusiastic about that. Would anyone be able to give me some info about how and why you can land off some waterfalls flat and others you have to 'pin it'. I guess this is a similar question to why do they have a machine blowing bubbles in the water for those big cliff diving competitions? Is it to do with surface tension or what's going on here? CHeers
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Old May 2nd 2014, 04:07 AM   #2
MBW
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The amount of air bubbles in the water reduces it's effective density,
essentially are you hitting solid water or a foam.

The more air bubbles the lower the density, thus the lower the buoyancy forces trying to stop you going under, thus the lower the impact.

At the extreme, there could be so much air (and so little water) that you sink.
(It has been suggested that releases of methane bubbles from the ocean floor have been responsible for boats sinking).

I think that the bubbles in diving are primarily to make the water surface more visable, I don't think the volume of air involved is intended to make a significant difference to the water density.
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