Date: Sun, 24 Aug 2003 21:13:03 -0500

Author: "Matt Lowry"

Subject: Finding a good Cu plate

Post:

Zig et al,

Where can I find an alloy 101 disc that is 0.5" thick? McMaster-Carr
has only got 1" thick plates. Would a 6" diameter and 1" thick plate
work well? Thoughts?

Cheers,

Matt Lowry
Lake Forest High School
Lake Forest, IL


>>> peacock@physics.utah.edu 08/22/03 12:13 PM >>>


Tappers, those of you doing the cooled Cu plate with the big magnet need
to know this tip
from one of our Low Temp wallahs.
Apply a thin coat of grease to the back side of the CU plate and the
cooling time
DECREASES by a factor of 2, thats 1/2 the time for you former Marines.
I used silicone HiVac grease, ordinary grease works just as well.
This one of the all time nifty demos. Zig

Zigmund J. Peacock
WWW.physics.utah.edu/people/staff/peacock.html
University of Utah/Physics peacock@physics.utah.edu
115 SOUTH 1400 EAST #201 Tel 801 581 6602
SALT LAKE CITY UT 84112-0830 Fax 801 581 4801

"We sleep safely in our beds because rough men stand ready in
the night to do violence to those who would do us harm"
-- George Orwell

"All that is necessary for the triumph of evil is that good
men do nothing!"
-- Edmund Burke

From thomason@colorado.edu Sun Aug 24 23:01:32 2003
Reply-To:
From: "Michael Thomason"
To:
Subject: RE: Finding a good Cu plate
Date: Sun, 24 Aug 2003 21:03:30 -0600
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Matt,

Here http://www.onlinemetals.com/ is the source I'm using.

I special ordered 6x6-inch by 2-inch-thick plates. With two of them you can
fly a NdFeB magnet
http://www.exploratorium.edu/exhibit_services/exhibits/f/floating_copper.htm
l as Paul Doherty discovered. My faculty seem to enjoy this even more than
dropping the magnet unless the plate is supercooled.

As Paul pointed out back in April, skin depth is large for slowly
time-varying eddy currents. Three-inch plates might be even nicer.

Michael Thomason, Director, Physics Learning Laboratories
University of Colorado, Boulder, Department of Physics
http://physicslearning.colorado.edu
mailto:thomason@colorado.edu
303-492-7117

"Species of plants and animals are disappearing a hundred or more times
faster than before the coming of humanity, and as many as half may be gone
by the end of this century. An Armageddon is approaching... It is the
wreckage of the planet by an exuberantly plentiful and ingenious humanity.
The race is now on between the technoscientific forces that are
destroying the living environment and those that can be harnessed to save
it. We are inside a bottleneck of overpopulation and wasteful consumption.
If the race is won, humanity can emerge in far better condition than when it
entered, and with most of the diversity of life still intact.
...Surely the rest of life matters. Surely our stewardship is its
only hope. We will be wise to listen carefully to the heart, then act with
rational intentions and all the tools we can bring to bear."
E O Wilson, "The Future of Life"


-----Original Message-----
From: owner-tap-l@listproc.appstate.edu
[mailto:owner-tap-l@listproc.appstate.edu] On Behalf Of Matt Lowry
Sent: Sunday, August 24, 2003 8:13 PM
To: tap-l@listproc.appstate.edu
Subject: Finding a good Cu plate


Zig et al,

Where can I find an alloy 101 disc that is 0.5" thick? McMaster-Carr has
only got 1" thick plates. Would a 6" diameter and 1" thick plate work well?
Thoughts?

Cheers,

Matt Lowry
Lake Forest High School
Lake Forest, IL


>>> peacock@physics.utah.edu 08/22/03 12:13 PM >>>


Tappers, those of you doing the cooled Cu plate with the big magnet need to
know this tip from one of our Low Temp wallahs.
Apply a thin coat of grease to the back side of the CU plate and the
cooling time DECREASES by a factor of 2, thats 1/2 the time for you former
Marines.
I used silicone HiVac grease, ordinary grease works just as well.
This one of the all time nifty demos. Zig

Zigmund J. Peacock
WWW.physics.utah.edu/people/staff/peacock.html
University of Utah/Physics peacock@physics.utah.edu
115 SOUTH 1400 EAST #201 Tel 801 581 6602
SALT LAKE CITY UT 84112-0830 Fax 801 581 4801

"We sleep safely in our beds because rough men stand ready in the night to
do violence to those who would do us harm"
-- George Orwell

"All that is necessary for the triumph of evil is that good men do
nothing!"
-- Edmund Burke

From billb@eskimo.com Mon Aug 25 01:10:28 2003
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Date: Sun, 24 Aug 2003 22:12:36 -0700 (PDT)
From: William Beaty
To: tap-l@listproc.appstate.edu
Subject: Re: Finding a good Cu plate
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On Sun, 24 Aug 2003, Matt Lowry wrote:

> Zig et al,
>
> Where can I find an alloy 101 disc that is 0.5" thick? McMaster-Carr
> has only got 1" thick plates. Would a 6" diameter and 1" thick plate
> work well? Thoughts?


Hey, the local electronics surplus guy (http://www.houseofscience.com)
could do a run of custom copper plates for mail order. How many people
would be interested? What dimensions of plate would be best for demos?


That thing with the grease is amazing. Speed up the heat transfer by
INSULATING the copper? To prevent a gas layer from forming? Dead cool!
(So to speak.) I bet there's a better coating to use. Maybe glue on a
layer of something. Or use just the right thickness of silicone caulk.
Less messy that way.


Another possible experiment: cooling the copper pipe and dropping the
magnets through. I suspect that there is a "best" temperature for
maximizing the slowness of the magnet. After all, there probably is a
"best" conductivity. A superconductor won't slow the magnet's fall (it
will just push it into the center of the tube as it falls.) An insulator
won't slow the magnet either. Somewhere between them is the best
conductivity. You need a mechanical impedance-match to suck maximum KE
out of the falling magnet. I wonder of the maximum is below the
temperature of liquid nitrogen or above?


(((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb@eskimo.com http://amasci.com
EE/programmer/sci-exhibits amateur science, hobby projects, sci fair
Seattle, WA 206-789-0775 unusual phenomena, tesla coils, weird sci
From rueckner@fas.harvard.edu Mon Aug 25 08:11:29 2003
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