I posted this in another thread, and so if it's a duplication for you,
my apologies. TomGee is only one of several that post to this group
that are attempting to learn physics by using informal resources
available to them for free, with mixed success. TomGee, for example,
has a particular problem with the meaning of inertia, Newton's first
law, and whether F=ma and p=mv admits the possibility of F=mv (which
TomGee maintains is part of Newtonian physics). Below is a longish
extract from a beginning physics textbook and on a highly regarded book
on physics instruction. Though the context is the first law, it speaks
widely about many other similar contexts (relativity, quantum theory,
cosmology, the basic principles of doing science, among others), and I
copy it here as an object lesson for both who aim to learn and those
who aim to elucidate.
[I also admit to posting it in a new thread to be sure TomGee sees it.
:>)]
+++++++
From Physics: Principles with Applications, 5th ed., by Douglas C.
Giancoli, Prentice Hall, 1998, pg.78 and onwards:
=========================
What is the exact connection between force and motion? Aristotle
(384-322 b.c.) believed that a force was required to keep an object
moving along a horizontal plane. He would argue that to make a book
move across the table, you would have to exert a force on it
continuously. To Aristotle, the natural state of a body was at rest,
and force was believed necessary to keep a body in motion. Furthermore,
Aristotle argued, the greater the force n the body, the greater its
speed.
Some 2000 years later, Galileo questioned these Aristotelian views
and came to a radically different conclusion. Galileo maintained that
it is just as natural for an object to be in horizontal motion with a
constant velocity as it is for it to be at rest!
... It was Galileo's genius to imagine such an idealized world --
in this case, one where there is no friction -- and to see that it
could produce a more useful view of the real world. it was this
idealization that led him to his remarkable conclusion that if no force
is applied to a moving object, it will continue to move with constant
speed in a straight line. An object slows down only if a force is
exerted on it. Galileo thus interpreted friction as a force akin to
ordinary pushes and pulls.
... The difference between Aristotle's view and Galileo's is not
simply one of right or wrong.... The real difference lies in the fact
that Aristotle's view about the "natural state" of a body was
essentially a final statement -- no further development was possible.
Galileo's analysis, on the other hand, could be extended to explain a
great many more phenomena, and it provided a quantitative theory
allowing verifiable predictions.
... Upon this foundation, Isaac Newton built his great theory of
motion. Newton's analysis of motion is summarized in his famous "three
laws of motion." In his great work, the Principia (published in 1687),
Newton readily acknowledged his debt to Galileo. In fact, Newton's
first law of motion is very close to Galileo's conclusions.
==============================================================
From Teaching Introductory Physics, by Arnold B. Arons, John Wiley &
Sons, 1998, pg. and onwards:
==========================
Many presentations start in by ignoring the fact that the words "force"
and "mass," which in everyday speech, are heavily loaded metaphors, are
being taken out of everyday context and given very sophisticated
technical meaning, completely unfamiliar to the learner.... Students
have, in general, not been made self-conscious about, or sensitive to,
such semantic shifts, and they continue to endow the terms with the
diffuse metaphorical meanings previously absorbed or encountered. It is
helpful to make students explicitly conscious of the fact that the
words remain the same but that the meanings are sharply revised.
... Learners' difficulties in encompassing the law of inertia and
the concept of force stem in large measure from the wealth of common
sense preconceptions and experiential "rules" that most of us
assimilate to our view of the behavior of massive bodies before we are
introduced to Newtonian physics. Some of these views are Aristotelian
(e.g., the necessity of continued application of a push to keep a body
moving, it being very difficult to abandon thinking of rest as a
condition fundamentally different from that of motion, or to accept the
view that, rather than asking what keeps a body moving, we should ask
what causes it to stop), but many of these common sense views are more
closely related to the medieval notions of impetus associated with
names such as Buridan and Oresme.
All investigations show these "naive" conceptions to be very deeply
entrenched and very tenaciously held, and it is important for teachers
to understand that student difficulties are not reflections of
"stupidity" or recalcitrance. The difficulties are rooted in seemingly
logical consequences of perceived order and experience and are
vigorously reinforced by insistent use (or actually misuse) of words
drawn from everyday speech (inertia, mass, force, momentum, energy,
power, resistance) before these words have been given precise
operational meaning in physics. Persistent misuse of the terms in
thinking to oneself and in communicating with others is a major
obstacle to breaking away from the naive preconceptions.
... Investigations of understanding of the law of inertia further
show that it is far from sufficient to inculcate the law verbally and
supplement it with a few demonstrations of the behavior of frictionless
pucks on a table or gliders on an air track. Many students will
memorize and repeat the first law quite correctly in words but, when
confronted with the necessity of making predictions and describing what
happens in actual physical situations, concretely accessible to them,
they revert repeatedly to the naive preconceptions and predictions....
===============================================================
PD
.
|
