[arachne] Re: Best tip of the year

Arachne at FreeLists---The Arachne Fan Club!


SCUBA is very real world, and not a bit laboratory -- honest! 

  Absolutely.  However it's still a non-sequiter.

water proof even at only 30' depth (2 atmosphere's pressure at that
level)"
However, to answer your question: If a watch is rated at one atmosphere of pressure, that means you can go under water if you'd like but the watch can't survive. 

  Ok.  Let's start from the beginning:

When internal pressure and external pressure are equal, the amount of pressure experienced by the tank/watch is ZERO.

To illustrate this, think of an air compressor tank open to the atmosphere. The gauge pressure is zero, but we know that there there are 14.7 PSI inside, and 14.7 PSI outside (if we're at sea level on a "normal" day). It really doesn't matter if the internal pressure is 50 PSI and external is also 50 PSI. As long as internal and external pressures are equal, the pressure vessel "experiences" zero pressure.

Seal the tank. It's now like a watch. Internal and external pressures are still at equilibrium, and the pressure exerted on the tank/watch is still zero. Take the watch 32' under water. The pressure differential seen by the watch is 14.7PSI or 1 atmosphere.

What you've done above is analogous to inflating your tires to 20.3 PSI on your tire gauge because adding in the 1 atm (14.7 PSI) you actually have 35 PSI like it says on the side of the tire.

Arachne at FreeLists
-- Arachne, The Web Browser/Suite for DOS and Linux --

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