Date: Mon, 25 Feb 2002 09:12:11 -0700

Author: Jim Krider

Subject: RE: new demo: He balloons in liquid Nitrogen, quantitative

Post:

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We don't do this demo either.

Do you need to consider Hooke's Law for the rubber balloon? The bigger the
balloon the greater the force it exerts. Perhaps the equation should be PV
+ 1/2kx^2=nRT where x is the radius of the balloon.

Jim

-----Original Message-----
From: Steve Wonnell [mailto:wonnell@pha.jhu.edu]
Sent: Wednesday, February 20, 2002 11:45 AM
To: tap-l@listproc.appstate.edu
Cc: Steve Wonnell
Subject: new demo: He balloons in liquid Nitrogen, quantitative

Idea: Fill a balloon with helium, and insert it in a large pyrex beaker
filled with liquid nitrogen. Measure the liquid N2 level before and after
inserting the balloon to determine the displacement; this gives you the
approximate volume of the deflated balloon. Insert balloon in another
pyrex beaker of water at room temperature to determine the volume of the
balloon. If PV=nRT applies, if He is a fairly good ideal gas, and if the
pressure exerted by the nitrogen and water on the balloon is still
approximately 1 atmosphere, the volume should decrease to 77/300 (26%) of
its original volume; we measured 420/1170 (36%) the first time
around. But our measurements are uncertain to within 100 ml, so that's
420 plus/minus 100 ml, or about a 25% error. Now I need to work on a more
precise measurement of the liquid nitrogen volume--maybe by weighing
the beaker instead.

Anybody else do this demo?

Steve Wonnell

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=0D=0A=0D=0A EAD>=0D=0A rset=3Diso-8859-1">=0D=0A nge Server version 5.5.2655.35">=0D=0ARE: new demo: He balloo=<br> ns in liquid Nitrogen, quantitative=0D=0A=0D=0A=
=0D=0A=0D=0A

We don't do this demo either.  ONT>=0D=0A

=0D=0A=0D=0A

Do you need to consider H=
ooke's Law for the rubber balloon?  The bigger the balloon the g=
reater the force it exe
rts.  Perhaps the equation should be PV + 1/2kx^2=3DnRT where x =
is the radius of the balloon.

=0D=0A=0D=0A

=3D2>Jim=0D=0A

=0D=0A=0D=0A

-----Original =
Message-----
=0D=0A
From: Steve Wonnell [ REF=3D"mailto:wonnell@pha.jhu.edu">mailto:wonnell@pha.jhu.edu] ONT>=0D=0A
Sent: Wednesday, February 20, 2002 11:45=
AM
=0D=0A
To: tap-l@listproc.appstate.edu ONT>=0D=0A
Cc: Steve Wonnell=0D=0A
SIZE=3D2>Subject: new=20
demo: He balloons in liquid Nitrogen, quantitative
=0D=0A

=
=0D=0A
=0D=0A
=0D=0A=0D=0A

Idea:  Fill a =
balloon with helium, and insert it in a large pyrex beaker
=
=0D=0A
filled with liquid nitrogen.  Measure t=
he liquid N2 level before and after
=0D=0A
in=
serting the balloon to determine the displacement; this gives you the=
=0D=0A
approximate volume of the deflated ba=
lloon.  Insert balloon in another
=0D=0A
=3D2>pyrex beake
r of water at room temperature to determine the volume of the
=
=0D=0A
balloon.  If PV=3DnRT applies, if He is=
a fairly good ideal gas, and if the
=0D=0A
p=
ressure exerted by the nitrogen and water on the balloon is still NT>=0D=0A
approximately 1 atmosphere, the volume sh=
ould decrease to 77/300 (26%) of
=0D=0A
its o=
riginal volume; we measured 420/1170 (36%) the first time
=0D=
=0A
around.  But our measurements are unc
ertain to within 100 ml, so that's
=0D=0A
420=
plus/minus 100 ml, or about a 25% error.  Now I need to work on=
a more
=0D=0A
precise measurement of the liq=
uid nitrogen volume--maybe by weighing
=0D=0A
=3D2>the beaker instead.=0D=0A

=0D=0A=0D=0A

=3D2>Anybody else do this demo?=0D=0A

=0D=0A=0D=0A

SIZE=3D2>Steve Wonnell=0D=0A

=0D=0A=0D=0A=0D=0A L>=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=
=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=
=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=
=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=00=
=00=00=00=00=00=00=00=00=00

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