Pressure question

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From: Grace Limaye (gclimaye@comcast.net)
Date: Mon Nov 01 2004 - 13:50:44 PST 

Message-ID: <005001c4c05c$d736bef0$0200a8c0@HP610Home>
From: "Grace Limaye" <gclimaye@comcast.net>
Subject: Pressure question
Date: Mon, 1 Nov 2004 13:50:44 -0800

Every year in class, we do a classic demo called "Can Crusher". We boil a quart cup of water in an open aluminum soda can and then flip the can over top down into an ice bath. The can consequently implodes in the ice bath. We recognize that we create a very low pressure/vacuum situation in the can upon inserting it into the ice bath b/c the heated water vapor and air molecules contract downward as they lose heat to the ice bath. However, we are a bit confused as to how to describe the "net" pressure situation in the can as we heat the can on the hot plate.

Is it a weak low pressure situation b/c we are heating molecules in an open container (and causing a convection cycle) or is it a weak high pressure situation b/c we have air and water molecules escaping readily to the outside environment (from a relative high to a relative low pressure area)?

We would greatly appreciate your input!

Thanks!

Grace Limaye and Laurie Chandler
Sixth Grade Science
Menlo School

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