## Posts

Showing posts from March, 2009

### Cool 12 Second Math Tricks: Odd Areas

This one kinda speaks for itself: Cool 12second Math Tricks: Odd Areas on 12seconds.tv

### Where's 12?

A map view of 12seconds.tv ! Add it to you web page! Get the code here on the Google site . 12seconds clips mapped! on 12seconds.tv Where's 12 followup on 12seconds.tv

### Introducing Cool 12 Second Math Tricks: Logging Up

A big part of making math problems easier is recognizing simplification patterns. Hence, Cool 12 Second Math Tricks! More detailed steps follow each video Cool 12second Math Tricks: Logging up on 12seconds.tv Details 1. The first expression is the derivative of a logarithm. It's just a matter of seeing it. 2. Remember the chain rule vernocular: "The derivative of the whole thing is equal to the derivative of the outside times the derivative of the inside". You can read every little detail here at Wikipedia .

### 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:

### Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

Now available as a Kindle ebook for 99 cents ! Get a spiffy ebook, and fund more physics 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