Re: [Phys-L] force-pair question

[John Denker <jsd@av8n.com>]

  "Why do forces always occur in pairs?"

On 01/06/2015 05:09 AM, Anthony Lapinski wrote:

> Kids often want to know why things happen
> in the real world. 

Sure.  Kids and everybody else.

> My physics teacher in college remarked that "physics explains how, not
> why."
> I've always remembered this.

Right.  That is perhaps the most important concept in the
entire "conceptual physics" course.  Too bad the textbook
does not teach this concept, or anything remotely similar.

At some level, the correct response is to not answer, to 
deflect the question.  Usually the question "Why X?" should
be transmuted into something like
 -- "How do we know X, and how sure are we of that?"
 -- "How could we have predicted X?"
 -- "What else do we know that is related to X?

That is the response given by people who know what they are 
doing.  Such people seem to be well represented on this list.

We need to worry about the others.  Evidence suggests that
people who know what they are doing are few and far between.
I googled for the phrase
  https://www.google.com/search?q=%22Why+do+forces+always+occur+in+pairs%22
and got almost 2000 hits.

None of them supplied an answer involving the word
"evidence":
  https://www.google.com/search?q=%22Why+do+forces+always+occur+in+pairs%22+%22evidence%22

Also none involved "we don't know" or "nobody knows":
  https://ipv6.google.com/search?q=%22Why+do+forces+always+occur+in+pairs%22+%22we+don%27t+know%22
  https://ipv6.google.com/search?q=%22Why+do+forces+always+occur+in+pairs%22+%22nobody+knows%22

To repeat: science must explain /what/ happens.  It
may or may not explain /how/ it happens.  The basic
laws almost never explain /why/ it happens.  Teaching
this idea is waaaay harder than it sounds, because there
is an innate urge to look for the reason "why".  It's a
cultural universal, on a par with clothing.  The catch
is, if science does not fill this void, something else
will, and we probably won't be happy with the result.
There's a problem here that I do not know how to fix.

It has been suggested that Hewitt in the hands of a
/sufficiently good/ teacher will lead to good results.
I'm sure that's true, but it doesn't tell us what we
need to know.  It sounds like Stone Soup to me.  A 
small stone in the hands of a sufficiently good teacher
will also lead to good educational results.
  http://en.wikipedia.org/wiki/Stone_Soup
We need more nuanced, more incisive evaluation criteria.
Just now I added a section claiming that Hewitt's book
is to be criticized more for what it /doesn't/ say than
for what it does:
  https://www.av8n.com/physics/hewitt.htm#sec-missing

There are more than a few teachers who use no textbook at
all, and just hand out notes, plus pointers to online
resources.

I know it's hard to write a book, and even harder to
write a good book.  However, that's no excuse.  It
becomes a management issue:  Allocate enough resources
to solve the problem.  If it's a super-hard problem,
allocate more resources.  There exist organizations 
that routinely solve much harder problems than this.

If you took the money spent on common corpse marketing
and lobbying -- not the whole budget, just the marketing
and bribery (I mean lobbying) budget -- and invested it 
in writing some decent textbooks, we would be in a very 
different place now.

========================

Let's get back to the operational questions:  have you
ever asked students "Why do forces always occur in pairs?"
What do the answers look like?

Do your students actually read the book?  Do they /think/
while they are reading?  What percentage of them notice
that there is something fishy about the force-pair CONCEPT 
CHECK?

It would be nice to teach students how to handle bogus
questions.  Surely in the real world they will encounter
plenty of such questions.  If this skill is not taught in
physics class, where will it be taught?  You can't toss 
them into the deep end of this pool all at once, but you 
can teach the skill gradually........