Message-Id: <3.0.5.32.19990202215417.007aa320@lds.net>
Date: Tue, 02 Feb 1999 21:54:17 -0800
To: "Pinhole Listserv" <pinhole@exploratorium.edu>
From: "Bryan P. Hartley" <bhartley@lds.net>
Subject: Re: Pinhole Digest #130 - 02/02/99
In-Reply-To: <199902020820.BAA03541@mail.lds.net>
Eric, then why when I put a drop of soap in the water and then inverting
it, the card was not held in place and the water and card fell. Luckily I
did it over a sink. I suspect that the surface tension of the water plays a
bigger role than air pressure. Bryan Hartley
At 12:20 AM 2/2/99 -0800, you wrote:
>Pinhole Digest #130 - Tuesday, February 2, 1999
>
> re: air pressure demo
> by "Eric Muller" <emuller@exploratorium.edu>
>
>
>----------------------------------------------------------------------
>
>Subject: re: air pressure demo
>From: Eric Muller <emuller@exploratorium.edu>
>Date: Mon, 01 Feb 1999 14:22:02 -0800
>
>Boyle's law says (paraphrasing)- If you increase the volume of a gas, then
>you decrease the pressure of that gas in a closed system.
>
>When you do the inverted-card-on-the-glass-trick, the water yanks down just
>a bit and expands the volume of air above the water. This decreases the
>pressure of the air inside the cup (actually the entire contents of the cup
>has decreased pressure). The greater air pressure outside the cup is what
>holds up the card and liquid.
>
>
>
>Eric Muller
>Staff Teacher
>Exploratorium Teacher Institute
>3601 Lyon St.
>San Francisco, CA 94123
>
>emuller@exploratorium.edu
>415-561-0313
>
>----------------------------------------------------------------------
>End of Pinhole Digest
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