Matt,

Well, you know how physicists are - they like to find the cleverest solution to the most complex variation of a simple problem.

Dunkin your donut in 'latte has always worked but along came a bloke called Stokes and he said he had one solution for all problems:

Surface integral of partial S = Partial line integral of S. S is the donut of course, or your dog, a cow, a couch, the ocean or whatever strikes your fancy.

It took me forever to wrap my head around it but it finally sunk in one day. I explained it to my 10 year old son two years ago using an orange and nice chalkboard drawings..., he got it right away.

The beautiful young mind... Einstein did say all kids could learn partial differential equations easily before 8 years of age.

David

PS Donuts are notorious for their non constant diameter...