Calculating Eddy Currents

Some of the most popular magnet demonstrations highlight eddy currents. We’ll explore a formula that calculates the eddy current forces, and try to merge that theory with experimental testing. We hope to figure out how to estimate these interesting forces.

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[Ensivion]

I love this video, straight to the point, does actual science and shows the results.

[DiegoSpinola]

These guys aren't just great suppliers for magnets, they produce great educational content that can't be found anywhere else...

[stefanfoot]

How do you determine the shape factor?

[gaactic_muffin]

what would happen if you roll one of those magnetic balls along a sheet of aluminum? does it not work because the magnet might switch poles as it rolls?

[davidprock]

Can you do me a favor and see if carbon rods or graphite sheet has the same effects?

[sarakabani]

hello! when calculating the theoretical values for distance, how did you get velocity? on your blog, all the other values for the equation can be found except v!

[jeffscharpf]

What happens if you swap one magnet so the poles are not attracting? Does this cancel the eddy current and force?

[foxpup]

With the aluminium cart, I'd wrap rubber bands or something of the same effect arround the pivot mount of the castor wheels so they can be placed in and stay in the correct orientation. That way they don't have to align themselves on the way down, messing up the dynamics. :-) The wheels at 3:44 do not look "happy". :-)

[nrdesign]

I had the idea to brake an acidentally slamming door magnetically, and this might be the perfect start.

[jwlsiee]

Can anyone help me figure out what the shape factor would be for a cylindrical magnet? The paper cited seems to assume a rectangular magnet, so the closest I can get is a shape factor for a square.

[Jamesvandaele]

It is fascinating to me how many smart people there are that are exploring eddy currents for inducing drag and yet the one question on my mind seems nowhere. What metal (I assume it is a metal) produces the most magnetic drag when you keep the magnet as a constant. I would think this was fairly obvious or perhaps there is some fundamental reason that this doesn't matter when it comes to induction motors, but to my mind, the better you have magnetic drag, the more efficient the motor. I was thinking AG perhaps might be better than Aluminum. But for some reason I cannot even seem to find a comparison of Aluminum to Copper, although I think I saw in some engineering forum that everyone just knew copper to be better.

[whatitmeans]

Have you tried to model the eddy braking drag force using a sublinear damping?
being "v" the speed and "a" some constant, instead of a drag force following
F(v)=a*v
you could try

This kind of drag, since isn't locally Lipschitz, could allow your ODEs to have solutions of finite duration, meaning here that the solution will become exactly zero forever after a finite extinction time, something that is impossible for the classic physiscs models through ODEs that holds uniqueness of solutions.
As example of this solutions, think of the system
x'=-sgn(x)*sqrt(|x|), x(0)=1
which could hold the solution
x(t)=1/4*(1-t/2+|1-t/2|)^2
that becomes zero after t=2.

You could see that the proposed Force behaves like the linear term you have used for low speeds not too near zero, where in the origin has a sudden start similar to the results of your experiments, and it also resembles the classic quadratic drag force used in fluids mechanics for large speeds.

Hope you can play with it and comment if it suits your experiments (hoping it improve the accuracy).

[georgebazan]

They should make escalators that use Eddy Currents

[syrusjames]

By the way, the newton's equation can only be used when we have a constant acceleration. In this case the acceleration is not constant.

[zigmaex]

What is that distracting racket in the background? Is that noise from my computer? Radio interference?

[xushenxin]

you use English system, not metric. It is so disgusting...