Re: curve balls, airfoils, greenhouse effect

[palmer@sfu.ca (Leigh Palmer)]

> However, I won't abandon the greenhouse effect description since it does
> seem to help students grasp the global greenhouse effect.

You certainly shouldn't abandon it, and you should call it the greenhouse
effect, and you should apply it to planetary atmospheres. Explain that the
name is a vestige of a nineteenth century misconception that greenhouses
worked that way, but it has long been known that they don't. That should
lead the students to ask "How do greenhouses work, then?" Am I alone in
welcoming questions from students? Getting them to ask such questions is
the primary goal in all my teaching. This topic is a lead pipe cinch to
evoke questions; I always use it.

> This is one of
> the few topics that I can ask the question "EXPLAIN--" and NOT get
> gibberish back from half the class.  It seems to me to be sufficient to
> present the 'standard' explanation and then add that this effect is
> _greatly_ enhanced in real greenhouses and cars by the lack of convenction
> cooling.  That's not a LIE --IMO.

It is at the very least distortion of fact. You should point out that it
is an unmeasurable (or at least an unmeasured) effect in greenhouses. You
should tell them that many greenhouses are constructed today using
polyethylene and other plastics that transmit infrared as well as they
transmit visible light. What is wrong with telling the unvarnished truth?

> I'm not ready to give up Bernoulli on airfoils yet either.  Again,
> calculations give reasonable numbers, and I really haven't heard or seen a
> description that negates Bernoulli as a _major_ factor in LOW SPEED
> airfoils--again such as those used with human-powered craft.

I agree with you. That is reasonable. Now you are electing the truth for
a reason I can't fathom in light of what you've said above. The Gossamer
Albatross flies differently from an F-15, so differently that utterly
different physics is appropriate to the description of the phenomena. I
think students are capable of appreciating that fact. I find I am much
more comfortable telling them what I believe to be the truth.

> I'll TRY to refrain from any more comments on these threads.   <ggggg>

I tried too. It didn't work.

Leigh