Anti-Gravity Tube
"An eddy current is set up in a conductor in response to a changing magnetic field. Lenz's law predicts that the current moves in such a way as to create a magnetic field opposing the change; to do this in a conductor, electrons swirl in a plane perpendicular to the changing magnetic field. Because the magnetic fields of the eddy currents oppose the magnetic field of the falling magnet; there is attraction between the two fields. Energy is converted into heat. This principle is used in damping the oscillation of the lever arm of mechanical balances."Ummmmm OK. Magic.
Labels: Cool Beans
posted by Xavier at 8:29 PM
10 Comments:
The first thing that popped into my head upon reading that description was, "Newton's 1st gets a boost via magnetic fields."
The first thing that popped into my head upon watching the video was, "That's so cool!"
Thanks for the laugh, Xavier.
A witch! A witch!
So, if I understand the video, it is slowing down the fall through the tube....the same as dampening the motion of oscillating scales, etc...
The fact is, we understand so little about the origins of magnetism, that once we begin to grasp the molecular application, we will have a source of power that will provide endless anti-gravity power and travel....Maybe in the next 100 years....?
Of course! Why didn't I think of that?
*laughs*
Eddy currents can be very handy things if one is interested in detecting flaws in metal structures. They also make for cool videos like this one!
Jim
Yea, that's the only practical use as far as I know, dampening scales (not sure of the rest of your comment, Bion). If you have a non-digital reloading scale there ought to be a part where a piece of aluminum is put between a few strong magnets to allow the scale to settle faster.
I do a demo with the magnet out of a hard drive and a sheet of 1/8 inch plate aluminum
There's really nothing all that mysterious about it. I use a similar demo in my physics classes all the time. The falling magnet pushes around electrons in the tube. These moving electrons create a magnetic field which repel the falling magnet (think north pole to north pole repulsion).
A changing magnetic field will induce a current inside a conductor. The current will exist in such a manner as to create an induced magnetic field opposite the magnetic field of the falling magnet.
The faster the magnet moves through the conductor, the larger the current is, the larger the induced and opposing magnetic field is. Thus, if the magnet is falling quickly through the pipe, there's a lot of force opposing it, if it falls slowly, there is little opposing force.
As the induced magnetic field is opposite of the field generated by the falling magnet, it's always slowing the magnet down.
What all of this means is that the magnet at first falls quickly, and is strongly opposed by the induced magnetic field, so it slows down. As it slows down, the induced magnetic field decreases, but the force due to gravity remains constant, and it speeds back up. This in turn, creates a strong magnetic field, that slows the magnet down. This repeats until the magnet falls out of the tube.
Magnetic induction can and has been used to generate power. As a simple example, there are flashlights with a magnet surrounded by copper wire. As you shake the magnet inside the copper wire, you induce current on the wire that you store and then use later to power the flashlight.
Neat, huh?
The speedometers and tachometers in older applications used eddy currents. Usually a magnet was rotated by the device being measured. It was located inside a copper cup attached to an indicator needle. As the magnet rotated it produced a torque which was opposed by a spring on the cup. Faster rotating magnet, cup tried to turn further against spring pressure, needle moved further.
Eddy current is also the thing that keeps the disc in your electric meter from spinning too fast.
It's a neat phenomenon because you can have a speed-proportional braking force with no physical contact.
MC
Another very practical application is that "eddy current brakes," are used on mining cars instead of friction based brakes.
Car manufacturers don't sell these on cars since they would essentially never wear out and they couldn't get their billions of dollars from replacement break parts. :(
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