On Tue, 25 Apr 2006 00:19:56 +0000, Christopher Tidy
wrote:

David Billington wrote:
Thanks Chris,

The last time I did this demo was for some friends using magnets
salvaged from some wedding corsage after a wedding I attended in
Holland. The florists had used small NiFeBn magnets taped to the flower
stem and another inside the lapel or dress to hold the flowers in place.
About 10mm diameter and 2mm thick, these were a nice fit in standard
copper tubing, 15mm?, and the increase in time taken to fall compared
to a non magnetic item was quite amazing. I grabbed all the unwanted
corsages and stripped the magnets, although they are not expensive these
days and readily available.

I have maybe 20 small trapezium shaped magnets from 500 MB hard drives.
I'm not certain of the composition, but I think it may be NdFeB. I used
some for a demonstration at a school a couple of years ago. They will
creep down a 3 mm thick aluminium plate inclined at 80 degrees at only a
couple of centimetres per second. The speed in an aluminium tube with 3
mm walls is about the same. You can do some fascinating demonstrations
with these magnets which aren't easily observed with weaker magnets.
They're great fun.

Best wishes,

Chris
Greetings Chris,
This is such a good demo that when a neighbor asked me if I could help
a friend's child with a science paper/demo this is what I thought of.
The cool thing about it was that the demo related to all sorts of
things. From generators to speedometers to scales. And the concept is
simple enough for most 8th graders to understand. The kid who I did
this for wasn't the brightest bulb when it came to science and I was
able to get him to realize how and why it behaved the way it did. The
new, strong, rare earth magnets are tons-o-fun and really show
graphically the effects of magnetism. Imagine how keenly observant the
first researchers into magnetism must have been when the only magnets
were lodestone. The first time I saw this and learned what it was I
was 13. The three beam scales in school had an aluminum plate that
passed between two magnets as the damper. When I took apart my first
speedometer, (from a VW), I saw a disc connected to the rotating cable
surrounded by an aluminum cup. After thinking about it for a second I
knew exactly how it worked and why the speedo was malfunctioning.
ERS