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Re: [Phys-L] Hydrostatics question



There is an interesting practical problem related to this. One can find the amount of gasoline in a fuel tank (like in an airplane wing) by dipping a hollow glass rod into the tank all the way to the bottom and then cap the open end of the rod with a finger. When you pull the rod out, you can see how much fuel is in the tank. The surprise is that the air in the top of the tube only expands enough to let the fuel drop a fraction of a millimeter - hardly affecting the reading.

Bob at pC
________________________________________
From: Phys-l [phys-l-bounces@phys-l.org] on behalf of Bill Nettles [bnettles@uu.edu]
Sent: Sunday, July 21, 2013 11:01 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Hydrostatics question

Note that they are using a specific gravity of quicksilver of 14. I don't know if that is "rounded" or was the accepted precision value in 1798. If I use 13.6 (modern typical "calculator" usage), I get a 2.323... about 2.5% diff, about 1.5 mm different from the 1799 answer.

It's a good opportunity to explain how mercury barometers work, practice conversion factors, etc.

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of John Denker
Sent: Sunday, July 21, 2013 6:15 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Hydrostatics question

On 07/21/2013 03:27 PM, Peter Schoch wrote:
1. What is the "modern" law/principle that gives: "...the spaces
occupied by the same quantity of air, are reciprocally as the
compressing forces..."

Ideal gas law. PV = NkT

As a corollary,
P1 V2
---- = ----
P2 V1

at fixed N and T.
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