Message-Id: <3.0.5.32.19990128173928.007a7dc0@lds.net>
Date: Thu, 28 Jan 1999 17:39:28 -0800
To: "Pinhole Listserv" <pinhole@exploratorium.edu>
From: "Bryan P. Hartley" <bhartley@lds.net>
Subject: Re: Pinhole Digest #127 - 01/28/99
In-Reply-To: <199901280820.BAA15827@mail.lds.net>
At 12:20 AM 1/28/99 -0800, you wrote:
>Pinhole Digest #127 - Thursday, January 28, 1999
>
> copper patina and air pressure demo
> by "Jeff Erickson" <jefferick@yahoo.com>
> Re: Pinhole Digest #126 - 01/26/99
> by "Ian Bleakney" <bleekers@ousd.k12.ca.us>
>
>
>----------------------------------------------------------------------
>The air pressure demo is very misleading. The card is really held on by
the surface tension of the water in the cup. If you try it first with plain
water, it works. If you add soap to the water, it doesn't. Bryan Hartley
>Subject: copper patina and air pressure demo
>From: Jeff Erickson <jefferick@yahoo.com>
>Date: Wed, 27 Jan 1999 16:24:31 -0800 (PST)
>
>I'm interested in finding the BEST way to put a green patina on copper
>which will stay on. I've tried some acids with mixed results...
>
>Also, remember the air pressure demo where you amaze your students by
>putting water in a cup, covering it with a card, inverting the whole
>set-up and then watch the card remain pressed against the cup...with
>no leakage of water. My understanding of the explanation was that the
>total force on the top of the card was less than the total force on
>the bottom because the weight of water in the cup exerted much less
>than the 14 psi exerted on every other part of the card. Wouldn't
>this only be true if there was a vacuum above the water in the cup?
>If there is any air in the cup, wouldn't it be at 1 atm, and add to
>the pressure exerted by the water...resulting in a wet counter and/or
>students? Is there another explanation?
>
>
>
>
>
>==
>
>_________________________________________________________
>DO YOU YAHOO!?
>Get your free @yahoo.com address at http://mail.yahoo.com
>
>
>----------------------------------------------------------------------
>
>Subject: Re: Pinhole Digest #126 - 01/26/99
>From: Ian Bleakney <bleekers@ousd.k12.ca.us>
>Date: Wed, 27 Jan 1999 21:45:55 -0600
>
>For the Physics of Music seeker:
>
>Try:
>
>Clarence Bakken
>Gunn High School
>Palo Alto, CA 94306
>
>He made an excellent presentation on the topic to some teachers in=20
>Oakland last Saturday (at Skyline High). I have his packet of=20
>curriculum if you are at all interested.
>
>Ian
>--=20
>=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=
>=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87=87
>
>Ian Bleakney
>Science Instructor
>Merritt Middle College High School
>Oakland, CA
>
>The word 'bipartisan' usually means some larger-than-usual deception=20
>is being carried out.
>
>=A0=A0=A0=A0 - George Carlin
>
>----------------------------------------------------------------------
>End of Pinhole Digest
>
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