[Phys-l] Misconceptions (was: caloric)

[John Denker <jsd@av8n.com>]

jbellina wrote:
> On the other hand, could it be that those same students think of  
> energy as caloric?  If that is the case would it be useful to name  
> the misconception so as to deal with it?

In my considered opinion, no, that usually isn't helpful, and
certainly isn't required, for the following reasons:

1) I can perfectly well _describe_ the most-common heat misconception
 using the words "thermal energy is (allegedly) separately conserved,
 separately from other forms of energy".  Giving the concept a name
 just adds one step of indirection.  Using the long-winded form takes
 only a few milliseconds;  I can afford that.

 I can dismiss this misconception using only a few additional words:
 "Push your hands together and rub vigorously, like /this/."

2) An _accurate_ description of caloric theory would be more complicated,
 far more complicated than the subject deserves, and I hate to give out
 inaccurate information, even about long-dead theories.  Lying about
 history is hardly preferable to lying about anything else.  It gives a
 false impression of the scientific process.

3) For some students, giving the concept a name confers on it an
 unhelpful level of seeming-dignity and seeming-importance.

4) In general, I find dealing with misconceptions to be a very
 tricky business.  It is all too easy to inadvertently teach the
 students how to _make_ mistakes ... instead of teaching them how to
 *avoid* mistakes.

 Also, it can be proved on theoretical grounds that for every correct
 conception, there is an infinite number of misconceptions.  One cannot
 even dream of covering them all, or even naming them all.

 Discussing misconceptions one by one is like hunting bacteria with a
 sniper rifle.  It's not efficient, and there is too much collateral
 damage.

 Some data on this:  In a talk I gave last week, there were 40 slides.
  a) One slide dealt with two misconceptions.
  b) Half of another slide contrasted one of those misconceptions with
   the corresponding correct conception
  c) Another slide dealt with four more misconceptions.


 There are plenty of other relevant misconceptions that I didn't even
 mention.  Instead, the key slide (c) was little matrix with observed
 facts as columns and theories as rows, showing that even a few facts
 suffice to instantly discredit a wide range of misconceptions.

 This is the "antibiotic" approach to killing misconceptions:  You've
 got to kill them _many at a time_, not one at a time.

5) I will sheepishly admit that I sometimes use misconceptions for shock
 value, usually when talking to an audience of know-it-alls (*not* naive
 students).  I bait my hook by putting up slide "A" full of well-"known"
 misconceptions, and when they are all comfortably agreeing with the
 slide "A" -- "yeah, yeah, we know all this" -- I jerk them awake with
 slide "B" that flatly contradicts slide "A".  I like this, because
 it teaches them to be skeptical, i.e. not to agree with everything I
 say (or anybody else says).  It also establishes my cred as somebody who
 knows nontrivial things about the subject.

 This technique is *not* appropriate in front of naive students.  The
 disadvantages far outweigh any possible advantages.  As James Randi likes
 to say, magic works by confounding our expectations.  You can't do certain
 types of magic in front of young kids, because they don't have the relevant
 expectations.