We're All In It Together

[Guest Lester Weevils]

Classic drama.

[subsonic]

They're from the government and they're here to help.

[Guest Lester Weevils]

Supposedly this one is in production or pre-production.

"What is wrong with you men? How hard can it be to destroy a continent?"

http://www.youtube.com/watch?v=ds0-2irdP4c

[Guest Lester Weevils]

A witty piece--

[Guest Lester Weevils]

It is commonly recognized that "Plan 9 From Outer Space" may be the worst SF movie ever. The following movie is not nearly bad enough to unseat "Plan 9 From Outer Space" but it is a noble also-ran in the bad movie competition--

[media=]http://www.youtube.com/watch?NR=1&v=Uv948FT2uvw[/media]

[Guest Lester Weevils]

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[Guest Lester Weevils]

Thunderbirds Are Go! (inspiration for Team America)

[media=]http://www.youtube.com/watch?v=jO-My-JjmI0

[Guest Lester Weevils]

[media=]http://www.youtube.com/watch?v=C-keZJfiiOw

[Guest Lester Weevils]

"Incontrovertible evidence that UFOs do in fact exist... Just kidding"
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[gjohnsoniv]

"Incontrovertible evidence that UFOs do in fact exist... Just kidding"

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Now what is the science behind that?

[Guest Lester Weevils]

Now what is the science behind that?

Hi gjohnsoniv. Its an interesting question that I'm too dumb to explain. Maybe days or weeks of study would bring it all back good enough to explain. It is a very interesting question and wish I had time to fully figure it out. Maybe if I ever retire there will be time for such thangs if there are enough brain cells left. Rare-earth magnets can be real strong which enhances the effect over ordinary weak permanent magnets. It can be even more dramatic with superconductors. There are spooky videos of various super-conducting magnetic demonstrations.

Been 42 years since the last physics class and it's easy to get tripped up on the oldest most basic principles. Some of the basic principles can be elusively subtle. The long-ago scientists who discovered the basics were dang smart. The man in the second youtube video gives a general explanation starting at 0:48. He says that the moving magnet acts like a generator, inducing electric current in the copper tube. He says the electric current in the copper tube generates a magnetic field which impedes the movement of the magnet falling thru the pipe.

Tools for proper analysis might include-- Left-hand rule is for motors and right-hand rule is for generators-- http://en.wikipedia....rule_for_motors

Also the solenoid interpretation of the right-hand rule might come in handy--

http://en.wikipedia....Right-hand_rule An electric current passes through a solenoid, resulting in a magnetic field. When you wrap your right hand around the solenoid with your fingers in the direction of the conventional current, your thumb points in the direction of the magnetic north pole.

I spent some time trying to write a coherent explanation of the effect in those terms but failed miserably and erased it all. Maybe you can figger it out better. The magnetic lines of force pointing northward travel in an outward direction, from inside to outside thru the copper cylinder walls from the south pole. The magnetic lines of force going into the magnet's north pole point northward going inward thru the copper cylinder walls from outside to inside in vicinity of the magnet's north pole. The magnetic lines of force near the midline of the magnet are near parallel to the copper cylinder and most likely do not induce much circular current in the copper cylinder in vicinity of the middle of the magnet. So this reversal of current direction/magnetic field direction, in the copper cylinder, in vicinity of the magnet's poles may be a factor, but I can't tonight get the polarities correct to explain a "slow fall". Too many brain cells are long gone and forgotten.

But here is an intuitive experiential explanation that may be relevant though hardly rigorous-- Nowadays do intro physics labs still have those handsome demo hand-crank generators constructed from an array of horseshoe magnets, beautiful brass and steel on a hardwood base? In my day they were basically the same thing as old rural telephone system hand-crank signallers, but prettier--

Those hand crank generators are fun. For one thing if you crank the crap out of the thing it will shock the pee out of a classmate touching the terminals. Also elegantly demonstrates the difference between potential/voltage, versus power/work. If nothing is connected to the generator a young fella can easily spin the crank real fast and generate an impressive high measured no-load voltage. But if you hook up a 100 watt light bulb the generator gets harder to turn. You have to supply more work to light up that light bulb. Therefore the generator crank gets stiffer than merely free-wheeling.

And then if you connect a big copper wire between the generator terminals, making a dead-short-- It gets real hard to turn the crank. You have to work yer arm real hard to deliver lots of power thru that dead short.

OK, so anyway a no-load or light-load generator is easy to turn. A heavy-loaded generator is hard to turn.

The magnet falling thru the copper cylinder is a linear electric generator which it is working into a dead-short. So it gets real hard for the magnet to fall thru the copper cylinder because it has to supply all that power dissipated by a dead shorted output inside the copper cylinder.

[gjohnsoniv]

I watched another video that explained it, kinda. Apparently there are things called eddy currents that go in opposite directions to the magnetic field the magnet is producing, which in effect I guess causes the magnet to move more slowly due to the opposite current? That's what I got out of it at least, not sure how correct it is though. Maybe an engineer will jump on and explain it in layman's terms.

[mcurrier]

Hey...Barry says that everything is ok!

[Guest Lester Weevils]

I watched another video that explained it, kinda. Apparently there are things called eddy currents that go in opposite directions to the magnetic field the magnet is producing, which in effect I guess causes the magnet to move more slowly due to the opposite current? That's what I got out of it at least, not sure how correct it is though. Maybe an engineer will jump on and explain it in layman's terms.

If you happen to run across a document or video which shows diagrams of the eddy currents and induced magnetic fields, please let me know. A physics student might find it a trivial exercise to explain. Nothing mysterious but I don't have a good enough grasp of the directions of the eddy currents to propose a self-consistent explanation more than "it has something to do with induced currents and resultant magnetic fields" which is a pee poor explanation.

It would be simpler to analyze for instance, if the cylinder is constructed as a stack of copper rings, with something like thin mica insulation between the rings. That would also complicate the analysis with capacitative reactance, though perhaps the capacitance would be a minimal issue compared to the other effects. Dunno. Ideally each ring would be rather narrow in relation to the height of the magnet.

What the "cylinder made of rings" would buy for simple-minded analysis, is that one might more easily figger out what happens to the induced current and magnetic field of each individual ring. Maybe I'm all wrong, but am guessing that the moving magnet would induce different direction currents in the cylinder, in vicinity of the north and south poles of the magnet. If the eddy currents would "stay put" and only go in a circular motion in each insulated ring it would maybe be simpler to understand. If it is true that different parts of the cylinder have different-direction eddy currents, then it would stand to reason that in a continuous copper cylinder (not the one made of stacked rings) current would also flow vertically between the different regions, and it is difficult to imagine what that might look like. Perhaps it looks like "maxwell's corkscrew"?

The simple minded solution I made last night would not brake the falling magnet, so there was most likely something wrong.

Or maybe that was a correct solution but time-delay "makes it work"? When you change a magnetic field, currents don't start up immediately. When you stop changing a magnetic field the current doesn't "stop on a dime". Similarly when you start up a current it doesn't "instantly" form its full-blown magnetic field, and when you stop a current the magnetic field doesn't instantly collapse.

Phase lags might make the polarities I guessed, actually work, but there's probably more to it.

Ferinstance if you insert a stop in the cylinder and only let the magnet drop a tenth of an inch, and you have capability of measuring the magnetic field and eddy currents. I believe the magnetic field would lag the start time of the magnet, and it would take a little time to collapse after the magnet stops. So the copper tube's magnetic fields lagging behind the position of the dropping magnet might have something to do with it.

[gjohnsoniv]

I'll see if I can't find it real quick and then put the link in this comment. I never actually watched this video with sound so I don't know what it's like. Anyway here is the link: http://www.youtube.com/watch?feature=player_embedded&v=kU6NSh7hr7Q

Edited June 13, 2012 by gjohnsoniv

[Guest Lester Weevils]

Thanks for the video, gjohnsoniv. Your video led to more good videos. Didn't know that youtube nowadays has so many great mini-lectures. Wish I could have found that set a few years ago. Had been trying to read articles on solar wind and was having "polarity" problems trying to figure out which directions you would expect charged particles to go in the local solar magnetic field, and the polarity of the magnetic field of streams of charged particles and such. Was trying to get a "gut feel" of how the particles would want to behave. It was hard to find basic info in a form I could understand at that time.

I was considering the magnet in the cylinder a solenoid problem, which ought to have made a reasonable explanation (though not a comprehensive explanation) if I'd not confused polarities. Imagining that the current would travel the circumference of the copper cylinder, as it does in a wire loop. The following link is the way i was trying to understand the problem.

This other fella covers the topic from a slightly different direction, equally interesting--

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The video you posted illustrates "vertical" current loops rather than "horizontal" current loops traveling around the cylinder's circumference. Interesting. Perhaps delta in the magnet's field lines' vertical vector component induces circumference current loops and delta in the horizontal vector component induces the "vertical" current loops?

[gjohnsoniv]

Not sure. I'll have to watch those videos when I get home and can turn the volume up on my computer.

[Guest Lester Weevils]

Yeah at the most basic level, opposite poles attract and same poles repel. So in order to slow down the magnet, regardless of the specific mechanism at work, you need the following conditions-- Assuming the magnet's north pole is pointing up, then the cylinder needs to generate a south pole local region facing the top of the magnet to attract and "pull up" on the magnet. And/Or the cylinder needs to generate a south pole region facing the bottom of the magnet to "push up" the magnet.

That video you posted and the videos I posted all explain the mechanism, but to my weak brain it remains a subtle thing that needs more thought to entirely "get it". It would be nice to have a good enough gut feel that one could predict what would happen in related but not identical situations.

I remember Faraday from physics class but don't recall Lenz. Maybe I was asleep in class that day. Or more likely, I tend to remember stuff that seems useful at the time, and maybe Lenz didn't sound useful enough to remember.

[gjohnsoniv]

I wonder what would happen if you put the magnet in sideways within the pipe. I'm assuming it would be pushed out in one direction, but I don't know. This might be something to try out later.

[Guest Lester Weevils]

What do you get if you allow a Birmingham AL fella to make a low budget SF movie? This--

http://movies.netflix.com/WiMovie/Interplanetary/70197404

If you like funny cheez, its a good flick. I had it slightly wrong watching the thang. Thought sure it must have come out of Atlanta, so was a couple hundred miles off. Second guess would have been New Zealand. New Zealand has rednecks almost as good as home grown in the south. Same twisted sense of humor.

http://interplanetarymovie.blogspot.com/

[Guest Lester Weevils]

News Alert! Chicago over-run by giant radioactive locusts!

[media=]http://www.youtube.com/watch?v=5VIsJR2QTB8[/media]

[Guest Lester Weevils]

A service called Crackle has lots of "legit" dilbert episodes on Youtube. They are set up to run about the same number of commercial breaks as on TV broadcast, but it is only inserting a rare commercial when I play them. Not something to complain about. Crackle supposedly has other stuff as well, but haven't looked into it as yet.

[media=]http://www.youtube.com/watch?v=T5o92PnWuO4[/media]

[Guest Lester Weevils]

Just now realized that Youtube has one of the finest SF and post-nuclear-annihilation movies ever made. Fabulous 1975 movie on a tiny budget, written by Harlan Ellison-- "A Boy and His Dog". I've been linking some cheeze and funny stuff, but this one really is a top-notch though little-known movie. It is pretty funny too, assuming you have a demented enough sense of humor.

[media=]http://www.youtube.com/watch?v=lh7PYGV-PKc[/media]

[Guest Lester Weevils]

Nerds gone wild.

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