"Don Klipstein" wrote in message
...
In article , Steve wrote:

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what does it do??

They are magic, aren't they? Have you tried the drop a magnet down a
copper pipe trick?

The magnet moving down the pipe induces eddy currents. These eddy
currents produce an electromagnetic force that resists the movement of the
magnet (with respect to the pipe) and does so to an extent varying
directly with the speed at which the magnet is moving. This slows down
the magnet.

At least this is what I have heard.

And aluminum tubes do this also, just not quite as much as copper ones
do. And I have seen aluminum tube stock.

Most other metals do this less, but I imagine that iron and lead pipes
may slow the fall of a close-fitting "rare earth magnet" a little in
comparison to nonconductive pipes.

Well, iron for sure.

On Tue, 22 Jun 2004 08:21:58 GMT, "Greysky"
wrote:

ever since I was a child, magnets have held a fascination for me. I've been
collecting them ever since. It used to be that you could always scrounge
loudspeakers for Alnico magnets. Then when the newer ceramic magnets began
to be incorporated into loudspeakers, it became a challenge to remove them
from their enclosures without breaking them. Now, I have to admit, I am
having a ball collecting the new 'super magnets' - like the ones inside hard
drives. There are also cool cylindrical magnets that you can get from inside
the heads of VHS machines. My question is does anyone know of other sources
either for Neodymium 'duper magnets', or strong ceramic magnets

Strip down an old microwave oven, but be careful of the HV cap, it may
still be charged. (about 1uF at 3000v !!!!) Every one I have found has
a bleeder resistor acros it, so is safe, but you never know.

Anyway, remove the Magnetron and pull it to bits, 2 nice "doughnut"
ceramic magnets await you.

Barry Lennox

One good way to make a dramatic experiment is to get two identical
Neodymium-Iron-Boron magnets, permanently demagnetize one by
subjecting it to heat, and comparing how they perform in the copper
pipe. You could look up the demagnetizing temperature[1] and rig up
a thermometer, but it's easier to hold a small compass near the
magnet as you heat it. You could also try degaussing it with a
powerful AC electromagnet.

[1] See irreversible demagnetization versus temperature curves
at http://www.component.tdk.com/eneor_mg.pdf

Also see:
http://www.scitoys.com/scitoys/scito...s/magnets.html
http://www.rare-earth-magnets.com/ma...agnets_FAQ.htm


--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
have an "impossible" engineering project that only someone like
Doc Brown can solve? My resume is at http://www.guymacon.com/

They are magic, aren't they? Have you tried the drop a magnet down a
copper pipe trick?

Hi, see some more experiments at
http://www.scitoys.com/scitoys/scito...html#magnetism

BR from Ivan OK1SIP

"Greysky" wrote in message om...
... My question is does anyone know of other sources
either for Neodymium 'duper magnets', or strong ceramic magnets that I may
be missing out on? Magnets like these come closest to being perpetual motion
machines we have yet to make, and I'd hate to have some just wind up into
the trash because I didn't know they were there :-)

Thanks.!

A retail source of super strong magnets is at http://www.abcmagnet.cz/

BR from Ivan OK1SIP

On 23 Jun 2004 03:04:40 -0700, (OK1SIP) wrote:

"Greysky" wrote in message om...
... My question is does anyone know of other sources
either for Neodymium 'duper magnets', or strong ceramic magnets that I may
be missing out on? Magnets like these come closest to being perpetual motion
machines we have yet to make, and I'd hate to have some just wind up into
the trash because I didn't know they were there :-)

Thanks.!

A retail source of super strong magnets is at http://www.abcmagnet.cz/

BR from Ivan OK1SIP

In the US, Edmund Scientific at http://scientificsonline.com/ has long
been a good source for all sorts of science "toys" like magnets.

Happy trails,
Gary (net.yogi.bear)
------------------------------------------------
at the 51st percentile of ursine intelligence

Gary D. Schwartz, Needham, MA, USA
Please reply to: garyDOTschwartzATpoboxDOTcom

In article , Steve Nosko wrote:

"Paul_Morphy" wrote in message
...

"JW" wrote in message
...
On Tue, 22 Jun 2004 13:06:08 GMT (Steve J.
Noll) wrote in Message id: :

Have you tried the drop a magnet down a
copper pipe trick?

I'll bite. What happens?

I'm guessing some EMF is induced.


...and... continue with the line of reasoning...

What does that EMF produce and where?...

Current in a closed loop or two in the pipe, and heat in the pipe.

- Don Klipstein )

"Don Klipstein" wrote in message
...
In article , Steve Nosko wrote:

"Paul_Morphy" wrote in message
...

"JW" wrote in message
...
On Tue, 22 Jun 2004 13:06:08 GMT (Steve
J.
Noll) wrote in Message id: :

Have you tried the drop a magnet down a
copper pipe trick?

I'll bite. What happens?
I'm guessing some EMF is induced.


...and... continue with the line of reasoning...

What does that EMF produce and where?...

Current in a closed loop or two in the pipe, and heat in the pipe.

Back up a bit. What does the current in a loop produce well before the heat
builds up?...
--
Steve N, K,9;d, c. i My email has no u's.

Steve Nosko wrote:
"Paul_Morphy" wrote in message
...

"JW" wrote in message
. ..

On Tue, 22 Jun 2004 13:06:08 GMT (Steve J.
Noll) wrote in Message id: :


Have you tried the drop a magnet down a
copper pipe trick?

I'll bite. What happens?

I'm guessing some EMF is induced.



...and... continue with the line of reasoning...

What does that EMF produce and where?...

Hmmm, sorta like a rail gun in reverse?

"Greysky" wrote in message
m...
ever since I was a child, magnets have held a fascination for me. I've been
collecting them ever since. It used to be that you could always scrounge
loudspeakers for Alnico magnets. Then when the newer ceramic magnets began
to be incorporated into loudspeakers, it became a challenge to remove them
from their enclosures without breaking them. Now, I have to admit, I am
having a ball collecting the new 'super magnets' - like the ones inside hard
drives. There are also cool cylindrical magnets that you can get from inside
the heads of VHS machines. My question is does anyone know of other sources
either for Neodymium 'duper magnets', or strong ceramic magnets that I may
be missing out on? Magnets like these come closest to being perpetual motion
machines we have yet to make, and I'd hate to have some just wind up into
the trash because I didn't know they were there :-)

Thanks.!



not that you would want to destroy one, but some PMI servo disk motors have six
to eight very large cylindrical rare earth magnets in them. IIRC they are about
1.5 inch diameter by 1/4 inch thick or so. I had one with a bad disk that
yeilded some of these a few years back.