Magnet Experiment

[JJPellin]

I was able to repeat an experiment I saw in a You-Tube video. I dropped a very strong magnet down through a piece of copper pipe. The magnet falls very slowly through the pipe. I found this fascinating. I had limited success trying to capture this on video. I would be interested in a technical explaination of this phenomenon.

Johnny Pellin

 

[BigInch]

Why use coiled wire. Can't you connect the meter directly to the pipe?

you must get smarter than the software you're using.

 

[waross]

WOW!!! A Gravity Generator! Sure it will heat the pipe. But heat energy will not exceed the potential energy of the weight of the magnet times the perpendicular length of the pipe.
eg: A one pound magnet times one foot elevation change in the copper pipe equals a maximum of one foot pound of energy. The stronger the magnet, the more of the potential energy is converted into heat energy in the pipe.

Bill
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"Why not the best?"
Jimmy Carter

 

[handleman]

Why use coiled wire. Can't you connect the meter directly to the pipe?

Of course you can connect the meter directly to the pipe. However, how would you then make the current go through the meter instead of just running around circularly in the immediate vicinity of the magnet like it wants to do?

-handleman, CSWP (The new, easy test)

 

[waross]

The old school automobile speedometers worked on the same principle. Likewise many zero speed switches, and eddy current brakes.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[bimr]

Lenz's law is named after Heinrich Lenz, and it says: An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original change in magnetic flux.

http://video.mit.edu/watch/physics-demo-lenzs-law-with-copper-pipe-10268/

 

[Skogsgurra]

BigInch/handleman

The resistance in the circular path beneath the magnet is much, much lower than the resistance in the wires and the instrument you connect to the pipe's ends. So there will be no current flowing in the external path.

A coil is the way to go. I recently needed to build many vibration pick-ups and used exactly that principle. The coil is a small relay coil and I used a piece of soft iron that moved inside the coil with a small magnet attached to the free end. The magnet also coupled the core iron rod to he surface I was measuring.

I tried to use MEMS accelerometers, but the coil/rod/magnet arrangement was quicker to build and cheaper, too. The only problem was how to calibrate the devices. I didn't need very precise calibration. +/-5% was good enough.

Calibration turned out to be very easily done. I just dropped the core vertically and measured induced voltage. Or rather the derivative thereof. I already knew the speed derivative (gravity constant g) so it was an easy matter to calculate sensitivity from V/s and g.See recording here:

http://gke.org/pub/files/Vibration_P_U_Calibration_1_w_comments.jpg

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

I was just in Tucson last week and attended a Gem and Mineral show there after I finished teaching my class. It was generally jewelry stuff and not that interesting to me, but at one booth there was a crowd of people milling around, so I had to check it out. They had a big table with a box of polished lodestones (magnetite) in square, sphere and tapered cylindrical shapes, selling for $5/lb. I could not resist and bought a bunch of the spheres and a few of the tapered cylindrical versions. I have them on my desk now, so as my coworkers have been pointing out, I am now obsessed with playing with my balls while I talk on the phone. But this weekend I'm going to get a piece of copper pipe and fool around with this experiment, I'm really looking forward to putting by balls into a pipe and watching them descend slowly...


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[JJPellin]

I have tried a few different versions of this experiment. I got some very nice cylindrical rare-earth magnets (1/2" OD by 1/2" long). Dropping those down a piece of 3/4" copper pipe works well. But, I found that adding copper couplings to the outside of the pipe makes it work even better. Two layers of copper must reduce the resistance and slow the magnet down even more. After that I bought a larger cylindrical magnet (1" OD by 1" long). Dropping that down a piece of 1" copper pipe is the best result yet. It takes over 8.5 seconds to drop 2 feet. I made up an identical cylindrical piece of steel to serve as a control to prove that air resistance was not the cause of the slow drop. I haven't tried adding couplings to the OD of that pipe yet.

We have a nice tank full of liquid N2 in the shop. I am also planning to see what effect it has to cool the pipe in liquid N2. This should further reduce the resistance in the pipe and slow it down even more.


Johnny Pellin

 

[dgallup]

jraef - I believe magnetite hoes not have a very strong magnetic field strength so it won't drop as slowly as a stronger magnet.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[stevenal]

When I was introduced to this experiment, the presenter used a cow magnet. With a lot of city folks like me present, he had to explain just what a cow magnet was. Might want to Google it if you don't know. A cow magnet happens to be a the perfect shape for traveling through pipes and bovines. I picked one up at the local feed store to keep handy for demos.

 

[JJPellin]

A note of warning to everyone: These magnets can be dangerous. I had the 1" by 1" magnet laying on my desk. I forgot and set my lap-top bag on the desk. The magnet stuck to the back of the lap-top. The hard drive was wiped and could not be recovered. I lost everything on that drive. Luckily, there wasn't much there. I will be storing that magnet more carefully in the future.

Johnny Pellin

 

[KENAT]

Wiped hard drives etc. is one thing, some of them have enough force that if you get parts of your body between the magnet and another magnet/ferrous item you can cause significant injury.

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[IRstuff]

You guys might find this interesting:

http://www.opensourcephysics.org/items/detail.cfm?ID=10327

It's a Java simulation of a magnet falling through a conductive ring

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