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Re: [Phys-L] Conceptual Physics Course



On 05/11/2012 10:36 AM, Jeffrey Schnick wrote:
So this time, I want to make a point of effectively communicating to
the students what my goals are, why I am doing what I am doing, and
why I am asking them to do what I am asking them to do. I think I
also want to spend some time on getting the students to think about
how they are learning.

Good plan.

For instance if a student struggles with something and eventually
figures it out, I want to talk about the tactic that the student used
to finally figure it out and have them think of that tactic as a tool
that they can keep handy and try to apply to other situations. One
of my points in this paragraph is to remind myself of your message
and realize that my plan to tell students what my goals are can
backfire on me if I am not careful.

It sounds like you've got the strategy figured out.

what do you and others do to foster the love of learning and
enjoyment of thinking you mentioned below?

Well, there is one big idea, plus ten thousand details.

You've already figured out the big idea, namely knowing generally
what it is that needs doing. Possible additional resources in
this department include:
-- It is worth re-reading Lockhart's Lament every so often.
http://www.maa.org/devlin/devlin_03_08.html
http://www.maa.org/devlin/LockhartsLament.pdf
He speaks in terms of mathematics, but the same ideas apply to
physics, namely the idea that there is an art to doing physics.
There is such a thing as physics with style, physics with panache.

-- It is worth re-reading Feynman every so often ... the big
red books as well as the biographical stories. Feynman had
lots of panache. He also was good about pointing out the
connections (e.g. "The Same Equations have the Same Solutions").

-- It is worth re-reading the PSSC Physics book every so often.
It doesn't have nearly so much panache, but it is a reminder
that it *is* possible to cover introductory physics and still
get the physics right.


As for the details, here are some tactical suggestions.

The first rule is: Don't teach wrong stuff.
This is a "zerg" problem: Any particular wrong idea is relatively
easy to avoid, but the currently-popular textbooks are so full of
nonsense that avoiding all of the errors gets to be a big job.
It is nevertheless important, because every time a student is
required to "learn" a nonsense fact, it reinforces the idea that
critical thinking is not allowed in school. This is a big deal!

As an example: In Hewitt's _Conceptual Physics_ section 38.4 it
emphasizes that «Light behaves like waves when it travels in empty
space, and like particles when it interacts with solid matter.»
A few sentences later we find «CONCEPT CHECK: What causes light
to behave like a wave? Like a particle?»

Sorry, that's not conceptual physics. It's not conceptual, and
it's not physics. All it is doing is asking for rote regurgitation
of what was said earlier on the page. This is incompatible with
any pretense of critical thinking.

Another thing to keep in mind: There is a proverb that says people
tend to overestimate the power of short-term change and underestimate
the power of long-term change. In that spirit, keep in mind that
the students have been trained for 12 years that thinking in school
can only get them into trouble, so the first N times you tell them
you /want/ to see critical thinking, they won't believe you. There's
no reason why they should. However, if you keep at it, eventually
they will come around.

Also: Remember that the teacher's #1 most-exalted responsibility is
to _pass the baton_ i.e. to get each student to take responsibility
for their own learning and their own life in general. Teachers and
parents etc. can *help* students meet that responsibility, but cannot
do it for them.

As a token effort in that direction, rather than assigning specific
homework exercises, assign a "menu" of exercises (such as questions
25 through 35 at the end of the chapter). Then say "pick one that
looks interesting and do it".

Rationale: This gives students a small push in the direction
of exercising some discretion, some personal responsibility.
It sends the message that the teacher is not trying to control
the student.

Some students will be familiar with this scheme. There are
some grade-school teachers out there who have been doing this
for 40 years. OTOH some of your students will have never seen
this before. Some will be freaked out by it the first time.

It is important that the student actually be free to choose,
with no repercussions for choosing "this" question instead
of "that" question. Otherwise it becomes the worst sort of
control, i.e. control with secret rules, where the student
has to play mind-games to guess what the teacher really
wants.

If you need them to do question 35, just say so. You can
tell them "choose /one/ of the first 34 questions and answer
that; then also answer question 35."

Eventually they will figure out that they are allowed
to do more than one of the first 34 question, as few
or as many as needed, to build up strength in preparation
for doing question 35 ... but that is a more advanced
concept. That can wait. All in good time.

Another possible tactic: As an in-class assignment, tell the
students "Turn to section 11.5 in the text. One of the concepts
in this section is profoundly wrong. Identify the wrong concept,
and explain why it is wrong. Suggest a way of rewriting the
passage to make it correct."

Rationale: In the real world, nobody gets paid to answer
multiple-choice questions (except maybe in certain minimum-
wage jobs ... would you like fries with that?). Real-world
questions tend to be quite underspecified and open-ended.

Further rationale: This really drives home the point that
they can't believe everything they read in the text (or
elsewhere). It teaches them to think for themselves.
See also
http://www.av8n.com/physics/thinking.htm

You have to do this in class; otherwise they can just google
the answer ... or share the answer from student to student.
And then there is the likelihood that the third or fourth
time you ask such a question, you find that some of them have
googled for lists of bugs and annotated their textbooks, so
this becomes more of a test of motivation and googling skills,
rather than thinking skills ... but if they are motivated
enough to do all that, you've already won the war so you can
just sit there and smile.

As a related point: Encourage them to ask questions. Encourage
them to identify errors in the text. Encourage them to push
back if /you/ say something that doesn't make sense. Send them
off to the drug store to find products that cannot possibly work
as advertised. It is not practical to be hyper-skeptical of
everything, so each person needs to develop an intuition about
whether something warrants a lot of skepticism or only a little.
This requires practice.

Also promote group brain-storming sessions, where the various
group members each contribute part of the solution to a problem.
For one thing, this approximates real-world teamwork situations.
Secondly, it improves their metacognition, because they get to
see other people's thought processes ... not just final results,
but intermediate steps and /processes/. Thirdly, there is
(usually) a motivational benefit, because folks who contribute
get to feel that they are helping their peers and getting
recognition from their peers. (This can backfire disastrously
if somebody starts to feel he is "carrying" a bunch of ungrateful
peers, so keep a close eye on the proceedings, especially at
first.)

Also: It helps to do real-world problems whenever possible.
This is exceedingly hard, because real-world problems are
complicated and it is all-too-easy to get mired in details and
lose sight of the pedagogical objective. However, just doing
hokey made-up exercises is even worse! It forfeits the objective
and the rationale for the course.

As a constructive example: One thing that's good to cover in an
introductory physics course is the emergency stopping distance
for a car. Tail-gating. Blind-gating. Dynamic friction versus
quasi-static rolling friction. Braking versus steering around
an obstruction.

More generally: IMHO it is well worth covering _scaling laws_
at every opportunity. How does stopping distance scale with
speed? How does fuel economy scale with speed? How does the
turning radius scale with speed? How does the period of a
pendulum scale with length? How does the centrifugal force
you experience on a playground swingset scale with the length
of the chains (assuming the angle of motion remains the same,
i.e. plus and minus 90 degrees)?
http://www.av8n.com/physics/scaling.htm

Scaling laws are simultaneously easier and more powerful
than most of the stuff that gets covered in "standard"
physics texts these days.

Most importantly: This allows you to make the point that
thinking about things the smart way is *easier* than thinking
about things the not-so-smart way. This is the point of
going to school: It allows you to cope with real-world
problems, quicker and easier and better.

As the bumper sticker says: If you think the cost of
education is high, compare it to the cost of ignorance.

As a related point: Pick some random adults and ask them what
they remember from high-school physics or college physics.
Ask them what they wish had been covered less or covered more.
(I didn't come up with the car-physics example at random. It
is a very common answer to the wish-for-more question.)

I almost hate to say it, but the phases of the moon does *not*
count as a worthwhile real-world problem for most people.
There is a small minority of people (including me) who are
curious about such things, but the rest of them don't care.
It has zero practical importance in their lives.

Feel free to teach about moon phases if you want ... but
if the retention turns out to be near zero, I will be
neither surprised nor worried.

FWIW I've seen six-year-olds with really good 3D spatial
visualization skills who could give a perfectly cogent
explanation of the phases of the moon, and of why there
is not an eclipse every month. I have no idea where such
skills come from. Maybe some people were ravens in a
previous life. There are entire books on the subject
of how to learn 3D spatial visualization skills. Just
because you can visualize it easily doesn't mean other
people can ... and the methods used in the typical
introductory physics course are not going to impart
such skills. Not even close.

For the CJ majors, there is obviously a treeemendous amount
of physics in crime-scene reconstruction and accident-scene
reconstruction.

For the music majors, there is plenty you can do with the
physics of sound in general, and the physics of musical
instruments in particular. A wonderful resource is
http://www.phys.unsw.edu.au/music/

For the fine-arts majors, there is a lot you can do with the
physics of color. Filters. Pigments. Colored lights. Human
color vision. I don't have any good references on the topic
of artists' paints and pigments. I know there is a lot of
confusion and nonsense out there. If anybody has any good
suggestions, please speak up!

For the business majors: A great deal of modern (post-1900)
physics is statistical. A great deal of business strategy is
statistical. Design of experiment uses essentially the same
ideas as optimizing a manufacturing process or a marketing
campaign:
http://www.av8n.com/physics/twelve-coins.htm

Given that many of them arrive with weak algebra skills, you
can safely assume they have little or no clue about probability.
You will have to budget some time for laying down a foundation
in this area.

More generally: In case it wasn't obvious: don't skimp on the
math. Algebra is "supposed" to be a college entrance requirement,
and in any case it needs to be a graduation requirement. If
you have to review it, fine. The physics motivates the math
and the math explains the physics.

Knowledge is a giant lattice of facts /connected/ to one another
by math and logic. If you need to know any particular fact,
you can recall it and/or rederive it by means of its connections
to other facts.

Tangential remark: Here is an example of the sort of thing
that makes my hair stand on end when I flip through Serway
and Faugn: They basically just assert the escape-velocity
formula. It would have taken only two lines of algebra to
derive it, quantitatively, but they don't bother. Instead
they mumble one sentence of not-quite-correct "explanation"
and then assert the formula. No thought, no reinforcement
of previously-learned principles, just another formula to
be learned by rote.

To me, this is the opposite of what physics is. I "know"
the escape velocity formula, not because I have memorized
it, but because I know that whenever I need it I can re-
derive it instantly ... and the derivation will be *more*
reliable than rote memory could ever be.

I also worry about the relevance. Most non-science majors
are not going to spend any big part of their life calculating
escape velocities ... and they know it, so it is hard to
get them excited about studying this.

Also: There are issues related to public policy, such as
depletion of fossil fuel reserves, climate change, et cetera.

=======

There are thousands of tactics you can use. Basically you
need to spend a good fraction of every day for the rest of
your life coming up with the appropriate tactic du jour,
defending against worthless and/or nonsensical stuff in
the textbook, et cetera.

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

Last but not least, the following idea is not quite a
strategy, but perhaps high-level tactic:

Figure out /in advance/ what you want to be on the final
exam. You are allowed to change it up to the last minute,
but even so, the discipline of figuring it out in advance
is well worthwhile.

Then design the course to make that exam doable.

When I am asked to judge a program, I almost don't care about
the stated goals, philosophy, principles, textbooks, or "standards
documents".... To a first approximation, all I need to see are
the tests. Why? Because those are the most direct and trustworthy
gauge of what the powers-that-be care about.

To a better approximation, I would like to know how
well the students are doing N years later, but that's
much harder to evaluate. That's a topic for another
discussion.