Saturday, February 13, 2016

Physics Youtubes

Geodesic Sphere

After staring at divided spheres all day, as in carved into triangles (windows), the concept of flux, charge flowing, blowing if you will, like the wind, lends itself to different pictures, than one of squares.

Squares are less happy on spheres.

The lines of latitude and longitude are not about making squares, much as we might kid ourselves.

Oliver Heaviside, same as in Heaviside-Gibbs (they collaborated), gets credit for the cuter form of Maxwell's Equations.

Charge density is the explosive content, which adds up to what emanates through all those triangles (Coulomb, Gauss).  Curl (swirl).  Magnetic flux (Faraday).

No accident early derivatives were named "fluxions" by Sir Isaac.

Here's an excerpt of something I posted to The Physics Learning Research List (, replying to my own post in this context.  One typo fixed ("tries" -> "trees").   

Date:  Fri, Feb 12, 2016 at 9:12 AM 
Re: entropy video

I think polling educators in a subject regarding publicly / freely available teaching materials on that subject is a great way to foment productive dialog.  

I know Entropy is uber-basic to the core concepts the Physics curriculum wants to communicate effectively, so why not sample specimens on that topic in particular?  

What I've noticed is that in contrast to the magnetic field concept, which starts in many cases with the whole Earth being magnetic, there's no generalization regarding the Entropy of the planet (Earth).  Is it (A) increasing  (B) decreasing or (C) the question makes no physical sense.

We've talked about photosynthesis as a means of mass impoundment i.e. the total weight of trees as fixed hydrocarbons (water and carbon both) accounts for a lot of mass in the biosphere, but then the biosphere itself is but a thin film of negligible mass. 

If one were arguing whether Earth was gaining or losing mass on balance, I'd hazard (A) gaining, because of infalling space matter, however miniscule.  More matter is coming in than leaving and that's what matters, or am I wrong?

But what about Entropy?  It's not a physical quantity but a measure in a phase space.

Clearly Earth is *not* an isolated system, quite the opposite:  it's plugged directly into a star for fusion power energy.  So there's nothing in the equations of thermodynamics that says Earth *has* to be gaining Entropy right now, at this point it its existence.  So I see where (B) decreasing *might* be a sensible answer.

In any case, the contrast is stark:  those topics with a "whole Earth meaning / interpretation" such as "magnetic field" immediately use the whole Earth as an example to anchor the concept.   The Youtube videos are notoriously silent on this question of the Entropy of the Earth, that I can find, implying (C) the question makes no physical sense.  Too bad if so.

Divided Spheres