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[Phys-l] real or at least quasi-real problems

Hi --

First let me give the answer, and then explain why the question
is important.

I occasionally watch the "Mythbusters" show on TV. The Mythbuster
guys have a childlike sense of what is fun ... so they're like
children with a budget, plus some engineering skill.

I mention this because the show very commonly stumbles (so to
speak) across physics problems.
-- Sometimes the problems are at the level of high-school
physics, such as the one about trying to swing a playground
swingset 360 degrees clear over the top. This starts out as a
thinly-disguised problem in energy management and centrifugal
-- Sometimes the problems are at the level of college physics,
such as the one about using sunlight and mirrors to set a
ship on fire, as the Archimedes myth would have it. This is
best understood if you know about f/stop, phase space (the
Liouville theorem and all that), and maybe the black-body
radiation laws.

Watching the show makes it very apparent that the Mythbuster
guys are not physicists. Very commonly they do experiments
that fail ... whereas a moment's thought about the physics
would have told you the experiment was going to fail *and*
would have revealed how a few small changes would have made
a big difference.

Here are some examples from the "360 swing" episode: First
they tried just swinging in the usual playground way, to see
how high they could get. They should have known waaay in
advance that wouldn't work, and that something would break
if they tried it. Well, sure enough something broke, and
one of the staff fortuitously escaped serious injury.

This leads to an interesting open-ended discussion topic: Ask
each student: How would *you* have handled this task?

Later in the same show, having switched from people to crash-
test dummies, they set the dummy in motion, i.e. a fairly large
swinging motion. Then, at the top of the swing, at the forward
end of the motion, they fired off a rocket to help the dummy
go the rest of the way around and over the top.

Again this leads to open-ended discussion topics: Ask each
student: How would *you* have handled this task?


IMHO discussion topics like this are very important, because
they allow us to address the fundamental motivational question,

The answers, of course, include:
-- Sometimes, knowing some physics allows you to solve problems
that other folks cannot solve at all.
-- Sometimes knowing some physics "merely" allows you to solve
problems relatively quickly and easily, while other folks must
solve the problems in more difficult ways.
-- Indeed sometimes knowing some physics allows you to stay healthy
in situations where other folks would get killed or injured.
-- Often this involves originality and creativity, finding new
solutions to old problems and/or solving problems that no one
ever solved before.

This is a serious issue, because 99% of classroom assignments do
not make these points! They are not even consistent with these
points! Most assignments are artificial, in the sense that the
student works out the answer to a question where the answer is
already known. In a real-world situation, the smart approach
would be to just look up the known answer, rather than working
it out. There is precious little scope for originality and/or

As a related point, this partially answers the question of how
physicists get jobs. The usual image of a working physicist is
somebody with a PhD working an a big fancy research lab. That's
not wrong, but it's not the whole story. It's clear that the
Mythbusters producer ought to hire a physicist. The salary
would be money well spent, several times over.

I'm not saying that open-ended discussion topics solve all the
world's problems. There are many devilish details. For one
thing, when having a discussion in class, a few smart students
can run away with the topic, leaving the others in the dust.
Also, topics are easily "burned" in the sense that after they
have been discussed once, they become just like the end-of-chapter
problems in the text: the easiest way to answer them is to
look up the /known/ answers that others have already given. Last
but not least, this assumes that the teacher is willing to work
hard ... rather than just looking up the "correct" answers in
the Teacher's Guide.

On the other hand, such discussions do serve a vitally important
purpose, and the details can be dealt with. In particular,
real life is a never-ending source of new problems, so if one
problem gets "burned" you can choose another. The Mythbusters
show alone probably generates new topics faster than you can
discuss them in class (given the other constraints on class