Path: utzoo!mnetor!uunet!husc6!bloom-beacon!gatech!udel!princeton!notecnirp!fmm
From: fmm@notecnirp.Princeton.EDU (F. Miller Maley)
Newsgroups: sci.misc
Subject: Re: Soap Bubbles
Message-ID: <9726@princeton.Princeton.EDU>
Date: 8 Apr 88 19:57:21 GMT
References: <631@amc.UUCP>
Sender: news@princeton.Princeton.EDU
Reply-To: fmm@notecnirp.UUCP (F. Miller Maley)
Distribution: na
Organization: Dept. of Computer Science, Princeton University
Lines: 22
Summary: Air expands when heated

In article <631@amc.UUCP> warren@amc.UUCP (Warren Omohundro) writes:
> Washing the jugs consists of putting a small amount of detergent
> water into the jug, covering the mouth of the jug with a hand, and
> shaking vigorously.  When you uncover the mouth of the jug, there is
> a noticable release in pressure.  My question: Where does the extra
> air pressure come from?
> It must have something to do with the formation of the soap
> bubbles, since repeating the procedure with plain water generates no
> extra pressure.  So what is going on?

I think this is an easy one.  If you use water that is hotter than
room temperature, then shaking the jug causes the water in the jug to
heat the air.  Consequently, the pressure increases; the soap has
nothing to do with it.  Due to the narrow mouth of gallon milk jugs,
most of the hot air will remain inside the jug when the soapy water
is poured out.  Hence repeated washings or rinsings will not produce
nearly as great an effect.  Try it with plain water first and see
what happens.  Also, try it with very cold water and see if you
don't get the opposite effect.
--
Miller Maley  609-987-2808 | ...!princeton!fmm | 3x10^5 km/sec. It's not just
Princeton Computer Science | fmm@princeton.edu | a good idea. It's the law.