Re: pinhole Hot Air

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From: John or Jan Lahr (johnjan@lahr.org)
Date: Sat Jun 14 2003 - 22:00:13 PDT 

Message-Id: <5.1.0.14.2.20030614225430.07b18bb8@mail.attbi.com>
Date: Sat, 14 Jun 2003 23:00:13 -0600
From: John or Jan Lahr <johnjan@lahr.org>
Subject: Re: pinhole Hot Air

At 03:22 PM 6/14/2003, you wrote:
>The exhibit explains that the heating speeds up the air molecules inside
>the balloons and makes them hit each other harder and further apart, so
>they weigh less, causing them to rise.

I hope the sign didn't say that! The molecules do move faster when heated,
which
increases the pressure within the balloon and causes the balloon to
expand. The
mass of the air within the balloon remains the same, but the volume
increases, so
the density is reduced. If the overall density of the balloon is less than
that of
the surrounding air, then the balloon will rise.

The increase in the size of the balloon may not be apparent from looking at
the balloon.

Cheers,
John

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