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Re: heat, centrifugal force, etc.



Hi,

John Denker wrote:

"Another example that leaps to mind is centrifugal
force. There seems to be a cabal of high-school
textbook writers who say "there is no such thing
as centrifugal force". Give me a break! Most
kids know quite well that centrifugal force exists;
they learn this first-hand before they get to
kindergarten, based on their experience with
playground merry-go-rounds."

It is clear that John is correct here from the point of view of physics. No doubt about it. However, there are some pedagogical issues at could be considered.

There is a lot of physics education research (PER) which shows that Newtonian concept of force is very hard for students to understand at any level of instruction (e.g. Hake 1998). PER has suggested many approaches to make learning more efficient. The approach I have tried out is to start treating forces arising from *interactions*. Force is defined to be a measure of strength of interaction between two objects. Interaction is always symmetrical; this is another way to state Newton's Third Law. For practical purposes it is useful to discern contact interactions from distance interactions. This approach seems to make it easier for students to identify different forces acting on a given object. Another favorable outcome is that it is easier for students to master Newton's Third Law when they think forces as interactions. I have data on this one and I intend to write an article about it.

Now you can see why centrifugal force is not used in the first exposure to Newtonian physics: centrifugal forces do not arise from interactions! There is no other object which would exert it. Of course I introduce centrifugal forces but only after the students are confident with inertial reference frames. My closure for high school mechanics is to discuss a merry-go-around from inertial and non-inertial reference frames. Phys-L among other sources have taught me not to ban centrifugal forces; they do belong to more advanced courses and modern physics.

Regards,

Antti Savinainen
Kuopio Lyseo High School
Finland
homepage: <kotisivu.mtv3.fi/oma/physics/>

References:

R.R. Hake (1998): "Interactive-engagement vs traditional methods: A six-thousand-student survey of mechanics test data for introductory physics courses," Am. J. Phys. 66,
64- 74. Online at <http://www.physics.indiana.edu/~sdi/welcome.html#z44>