### Coil Levitation with Eddy Currents

I tried out a little quickie experiment in the lab this afternoon. In short: a coil with a changing current, (AC), placed on a non-ferromagnetic conductor, like aluminum, will induce an opposing magnetic field and levitate. You can read all about the effect caused by eddy currents, on Wikipedia, and watch what happened in the lab here:

Unknown said…
Hi there,

I have been doing some research into magnetic levitation using eddy currents when I stumbled upon your video here: http://12seconds.tv/channel/dolphus/108842. It is the only video I could find of someone actually doing levitation - which is weird. So I was just wondering if you could answer a few questions about the setup of your experiment. It would be greatly appreciated if you could just tell me the schematics for you experiment:

Was it AC 60Hz 240V power?
Aluminium table you used underneath?
Insulated copper wire in the
Unknown said…
contd...

in the circle?
How many turns of copper wire? (just a guess of how much wire to use?

If you could answer these I would be grateful.

Lance
antigrav_kids said…
The power was 60Hz 120V regulated through a variac to about 30V. The coil is insulated magnet wire. I don't know, but I suspect there are about 300 turns. It's just an old coil I pulled out of the junk pile. The metal underneath is about 3/4 inch think aluminum.
Magic Tricks said…
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### Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

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The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla

to the nabla for another coordinate system, say… cylindrical coordinates.

What we’ll need:

1. The Cartesian Nabla:

2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:

3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:

How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differe…

### Division: Distributing the Work

Our unschooling math comes in bits and pieces.  The oldest kid here, seven year-old No. 1 loves math problems, so math moves along pretty fast for her.  Here’s how she arrived at the distributive property recently.  Tldr; it came about only because she needed it.
“Give me a math problem!” No. 1 asked Mom-person.

“OK, what’s 18 divided by 2?  But, you’re going to have to do it as you walk.  You and Dad need to head out.”

And so, No. 1 and I found ourselves headed out on our mini-adventure with a new math problem to discuss.

One looked at the ceiling of the library lost in thought as we walked.  She glanced down at her fingers for a moment.  “Is it six?”

“I don’t know, let’s see,” I hedged.  “What’s two times six?  Is it eighteen?”

One looked at me hopefully heading back into her mental math.

I needed to visit the restroom before we left, so I hurried her calculation along.  “What’s two times five?”

I got a grin, and another look indicating she was thinking about that one.

I flashed eac…