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

 

[GregLocock]

Thingies law, a current acts in such a way as to oppose the effect inducing it. That being said copper is non magnetic. so that doesn't help.

Cheers

Greg Locock


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[VEBill]

Eddy currents. The moving magnet generates currents in the conductor, those currents create an opposing magnetic field that causes it to move very slowly.

You can also roll little disk magnets down a length of angle aluminum. They roll amusingly slowly.

Great project for middle school students.

 

[SomptingGuy]

Explaining and then predicting the terminal velocity is the interesting thing as a school project. The velocity at which the gravitation force equals the force created by the interaction of the magnetic fields.

- Steve

 

[stevenal]

Lenz's Law.

 

[BigInch]

Didn't it get warm too?

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

 

[Compositepro]

The worlds most powerful magnet:

https://www.youtube.com/watch?v=QGytW_C6hR8

Watch the last minute of the video where it takes two minutes for an aluminum to fall 12 ft.

 

[JStephen]

A similar effect can be used as a dampening mechanism- seems like this is used on scales, maybe? Where a copper disk between two magnets will create drag proportional to the velocity.

 

[Skogsgurra]

"Didn't it get warm too?"

Not any warmer than if you just droped the magnet the same distance. Without Al or Cu.

Gunnar Englund

http://www.gke.org

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

 

[cswilson]

If you try to duplicate this experiment yourself, be very careful! The rare earth magnets strong enough to provide a really visible effect are strong enough to create literally bone crushing force. I have known people who had to go to the ER after fooling around with them.

 

[SomptingGuy]

"Didn't it get warm too?"

I thought the copper tube would warm up, not the permanent magnet. It has the induced current flowing in it.

- Steve

 

[JJPellin]

I dropped the magnet through a dozen times, quickly and could not detect any heat in the pipe. The induced current should create some heat. But, the current is so low and the copper dissipates it so well, that it is undetectable. This weekend I tried this with a 5 foot piece of copper pipe. It took the magnet over 7 seconds to drop 5 feet.

Johnny Pellin

 

[GregLocock]

Let's say the magnet weighs 2 oz, 50g, PE=mgh, so 12*.05*10*2=12J. One J is a disappointingly useless bit of energy, even 12 of them would hardly change the temperature of a 5 foot pipe

Cheers

Greg Locock


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[TheTick]

but think of the MARKETING OPPORTUNITY! Sell "pipe magnets" that heat your home with the power of plumbing!

 

[SomptingGuy]

I wasn't suggesting the temperature rise to be in the hand-warming range. Just suggesting that the (small amount of) stored potential energy would end up in the pipe, not the magnet. I wonder if that is true though. One of those interview questions that would get a thinker thinking.

- Steve

 

[GregLocock]

I wasn't saying it was a bad way of looking at it, it is just that JJPellin's experiment wouldn't be enough to disprove or confirm it.



Cheers

Greg Locock


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[zdas04]

What would you see if you wrapped copper wire around the pipe and connected it to a (mili)ammeter?

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[GregLocock]

I'm thinking farady cage, much better to use a plastic pipe with wire around it. Then you've built a linear dynamo.

Cheers

Greg Locock


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[handleman]

<quote>What would you see if you wrapped copper wire around the pipe and connected it to a (mili)ammeter?

-handleman, CSWP (The new, easy test)

 

[handleman]

Dangit, sorry...

What would you see if you wrapped copper wire around the pipe and connected it to a (mili)ammeter?

I'm just an ME here, but I'm pretty sure the magnet would fall much faster, and you might see a blip on the ammeter. The magnet would have to induce current in the entire wire rather than a localized current in the big fat copper cylinder. Much more resistance means much less current, which means much less opposing magnetic field.

-handleman, CSWP (The new, easy test)