Re: [Phys-L] Dirigible Flight Question

[brian whatcott <betwys1@sbcglobal.net>]

On 11/5/2012 7:42 PM, John Denker wrote:
> On 11/05/2012 04:11 PM, Paul Nord wrote:
> > Ok, ok.  I'll give you the real question.  We've gotten bogged down
> > in dirigibles and blimps.
> >
> > I have altitude data for a weather balloon which picks up enough ice
> > at a 5 km altitude that it begins to descend.  It continues dropping
> > until it reaches about 2 km where enough ice has melted to allow the
> > balloon to continue its ascent.  We know the lift of the balloon.  We
> > know the mass of the payload.  What is the mass at the two points
/snip/

> > I hope everybody involved can now see the advantage of asking the real
> > question.  For starters, from my point of view, the non-real questions
> > tend to be an enormous waste of my time.  From the other party's point
> > of view, the real question is vastly more likely to generate a real
> > answer, a usable answer.
> >
> > This is the sort of thing that gives ivory towers a bad name.  Often
> > the non-real question is both more difficult and less useful than the
> > real question.  When I see textbooks devoid of real-world topics and
> > instead full of made-up nonsense, I want to tear my hair out.
It's not every time that a Denker post resonates, but when the talk 
turns to real world - I  listen.     It's such an obvious exit from the 
land of ideal physics.....
However, when I mentioned one real world application of real world high 
school geometry - how to get a 10 ft wheelbase vehicle with a 1 foot 
clearance over a high wall with 45 degree ramps - there was only one 
effort to provide an answer that nodded to geometry - but the flat top 
answer was plainly wrong.

Brian Whatcott      Altus OK