Message-Id: <3.0.5.32.19990201142202.008e2b90@192.174.2.1>
Date: Mon, 01 Feb 1999 14:22:02 -0800
To: pinhole
From: Eric Muller <emuller@exploratorium.edu>
Subject: re: air pressure demo
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