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Re: Vacuum sealed back
In Response To: Re: Vacuum sealed back ()

Hello James,

I just did a calculation and was very surprised to find that the dynamic pressure when swimming is actually insignificant!

If the "density" of water is 62.4 lb/ft^3 then the static pressure at a depth of 150 ft is 150*62.4/144 = 65 psi.

The dynamic pressure is half rho v^2 where rho is the density in proper English units = 62.4/32.2 = 1.94 slug/ft^3

So if you swish your watch through water at 10 ft/s then the dynamic pressure is 0.5*1.94*10^2 = 97 lbf/ft^2 = 0.67 psi which is almost nothing. At 100 ft/s it would be 67 psi. So you would have to be in a speedboat going nearly 70mph with your hand in the water to feel a dynamic pressure equivalent to the static pressure down at 150 ft.

Wow! I'm sorry I didn't do this calculation before I opened my mouth! I was totally off the wall! Please forgive me for misleading you.

You have a good point about not letting soap get to the seals.

Best wishes,

GT

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