[TCML] hoop stress in primary coil

[jimlux]

Lau, Gary wrote:
> OK Jim, I'll bite.  What's hoop stress?  Maybe the thing that annihilates the work coil in quarter-shrinkers?
> 

exactly.  hoop stress, generically, is the circumferential force on 
something round (e.g. the stress on the wall of a pressure vessel or 
pipe is mostly hoop stress)

ANd, yes, that's what causes the work coil on a quarter shrinker to 
deform/explode.


It's funny, in basic E&M, you cover the fact that a current in a loop 
causes the coil to want to expand (heck, it was on the Physics AP test 
back in 1976), but none of the basic texts actually do a numerical 
example.  That tells me it doesn't have a "nice" simple precise 
analytical solution.  (hmm magnetic fields, it's round, the solution 
probably involves Bessel functions).  But, just like the Wheeler 
formulas, I'm hoping someone has run across a simple approximation.