Re: [Phys-L] physics and potatoes

[John Denker <jsd@av8n.com>]

On 01/14/2015 07:05 AM, Folkerts, Timothy J wrote:

> The solution is about SERVING potatoes, not BAKING them.  If Hewitt
> is answering a different question than he himself asked, then he was
> DOUBLY confusing.  If Anthony was mis-remembering ("I saw a question
> in Hewitt about why potatoes are wrapped in foil for _BAKING_".),
> then all of a sudden Hewitt seems considerably more intelligent.  (I
> don't have the book to check.)

Hewitt's question is:
	In terms of physics, why do restaurants serve 
	baked potatoes wrapped in aluminum foil?

The word "serve" changes a few details ... but it does not 
get Hewitt off the hook.

This is supposed to be a real-world rich-context problem.
Students are supposed to use their knowledge of the real
world in order to answer the question.  This should be
obvious from the fact that the question does not specify
the thickness of the foil, the thermodynamic properties
of aluminum, or even the temperature of the potato.  Cold
potatoes are perfectly edible, as in potato salad.

It is a travesty to pretend that potatoes are wrapped in
foil /after/ baking.  In restaurants, wrapping potatoes 
is highly atypical, and wrapping them after baking is 
orders of magnitude more atypical.

If the question meant to ask about wrapping after baking,
it could have spelled that out.  If it meant to ask about
a scenario where you are cooking over a Wild West campfire
but nevertheless have lots of aluminum foil available, it
could have spelled that out.

It is all-too-common for Hewitt to use fake data.
 -- An exercise asks about a «jumbo jet with a mass of 30,000 kg.»
 -- A sidebar says: «Suppose an airplane flying normally at 
  80 km/h ...»
 -- et cetera


There are two possible sets of rules.  Take your pick:
  a) You can create imaginary scenarios and spell out all
   the details, e.g. the spherical cow in the ivory tower.
  b) You can ask students to apply their knowledge of the
   real world.

You can play by one set of rules or the other, but it
is grossly unfair to students to switch from one set
to the other without telling them which is which ...
and even more unfair to ask them to apply real-world
knowledge to things that don't exist.