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Grumble
 Posted on Tuesday, November 9, 2004 - 7:21 pm:

I experimented for a little while once my order of 20 N40 1/2" magnets came in, and as I kept adding magnets (up to 4) I didn't see a really great increase in velocity for the steel ball. What would be the optimal spacing for the magnets? Perhaps they are too close together? Also, will any of the later magnets in the series be shattered or is 20 in the 'safe zone'? Anyone know what kind of velocity I would get? My aim is to build a relatively fearsome accelerator.

-Grumble

Simon Quellen Field (Sfield)
 Posted on Tuesday, November 9, 2004 - 10:33 pm:

You can't afford enough magnets to get one to shatter in the gauss rifle.
You also can't afford enough magnets to become fearsome.

The 4 magnet gun throws the ball at about 15 feet per second.
A cheap rifle from Kmart throws a slug at about 4,000 feet per second.

Each magnet adds energy linearly. If four magnets produce 1 unit of
kinetic energy, 16 magnets will produce at most 4 units of kinetic energy.
But since kinetic energy is ½ mass times velocity squared,
to get twice the velocity, we will need 4 times the energy.
Thus 16 magnets will be needed to double the speed, assuming no friction
losses, and optimal placement.

So, we can complete a table of speeds versus number of magnets:

 speed number of magnets 15 fps 4 30 fps 16 60 fps 64 120 fps 256 240 fps 1024 480 fps 4096 960 fps 16384 1920 fps 65536 3840 fps 262144

I would be happy to sell you a quarter million magnets at 3 dollars
each. I will need some time to manufacture them, and payment in

By the way, if it takes one second to set up the two balls on a magnet,
it will take over 3 days to load the gun. If each magnet is 2 inches
from the last one, the gun will be over 8 miles long.

All of this assumes no friction, and assumes that the optimal distance
between magnets is always the same. It seems unlikely to me that 16
magnets will produce twice the velocity of 4. Experiment, and post
your results here. This would make a good science fair project.

Kevin H
Unregistered guest
 Posted on Sunday, May 8, 2005 - 6:55 pm:

Eh-hem...what about the magnets from FORCEFIELD? They have NdFeB magnets up to 2 inches diameter and 1 inch thick. Try http://www.wondermagnets.com/cgi-bin/edatcat/WMSstore.pl?user_action=detail&catalogno=0072 ...
I bet one could beat those figures with these magnets!!!

Simon Quellen Field (sfield)
Senior Member

Post Number: 386
Registered: 12-2004
 Posted on Sunday, May 8, 2005 - 7:15 pm:

Actually, no.

The magnets and the balls should be close to the same mass,
or you get reflected energy. A billiard ball will hit another
and stop, sending the other one on its way. But a BB will just
bounce off of a cannonball. This is called an impedance
mismatch.

The strongest magnets available at this time are the N50's we
have in our catalog. When stronger ones are available, we will
carry those. We have found that the nickel plated magnets don't
hold up to repeated impacts from the balls -- the nickel plating
is brittle and flakes off. The gold plating is very soft and
malleable, and just gets pounded into the magnet more securely
with each impact. The epoxy coated magnets are also prone to
the coating flaking off.

Besides, your assumption that a bigger magnet will somehow allow
you to get around simple arithmetic is unfounded. Even if you
could improve on the speed of the four magnet rifle, doubling
the speed there still means that you will need 65,536 magnets
to get over 3,000 feet per second. And since there are currently
only 9 of those \$40 magnets in stock, you would do better with
our much less expensive magnets anyway. Although I'm sure they'd
love to sell you \$2,621,440.00 worth of magnets...

Jeremy Denton (Unregistered Guest)
Unregistered guest
Posted From: 64.12.116.130
 Posted on Tuesday, October 11, 2005 - 5:57 pm:

Where can I find 1/2 inch gold plated magnets? I have checked a number of web sites and all I could find were tiny ones.

Simon Quellen Field (Sfield)
Senior Member

Post Number: 753
Registered: 12-2004
 Posted on Tuesday, October 11, 2005 - 7:11 pm:

Try our catalog.

surendra murthy.c (Science_boy)
New member