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Suppose that:

  • Temperature is stable.
  • Atmosphere pressure at mean sea level is 1013hpa.
  • I have a water proof barometer.

Would the barometer reading be different between the following two scenarios?

  • Submerged in the sea, 10 meters below surface.
  • Submerged at bottom of a 10-meters deep pool, the pool itself is situated 1000 meters above sea level. The pool is exposed to the atmosphere.
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3 Answers 3

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Yes the reading will change.

The barometer is telling you the total weight of all the stuff above it - specifically the total weight of stuff per unit area. If the amount of stuff changes then the reading on the barometer will change as well.

So the barometer in the pool will read a different pressure from the barometer in the sea. Both have the same weight per unit area of water above them, but the barometer in the pool has less air above it and will therefore give a lower reading.

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An additional consideration is that sea water has a higher density than pool water so that the under water barometer under the sea will read a higher pressure than the higher altitude under pool barometer, for two separate reasons. Higher water pressure due to salt water density+Higher air pressure due to lower altitude is greater than fresh water pressure + higher altitude lower air pressure.

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  • $\begingroup$ Yes, good call, that's true. You'd have to put sea water in the pool for it to be a fair comparison. $\endgroup$ Apr 30, 2015 at 7:05
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At sea level the average atmospheric pressure is 29.91" Hg. That is equivalent to 760mm or 76.0cm. If 33' of seawater is 1 atmosphere then 33' of seawater equals 760mm Hg. It follows that 1' of seawater would equal 23mm Hg (760/33=23)

1 Atm (at the surface) x1 liter should= 2 Atm (at 33') x 1/2 liter 1 x 1 = 2 x 1/2

So it follows that any variation to the average of the atmospheric variable would in fact be detectable underwater.

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