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Re: [Phys-l] Inertia?



Many demonstrations can have problems, and the one with the chairs in the
truck was not an exception. The BIG problem with this demo is that students
generally remember the dramatic parts of the video and do not retain the
concept that you are targeting. See the research of Catherine Crouch.
There is some evidence from cognitive science that movies and simulations
really do not work better than static pictures. The one exception is where
the simulation can make visible underlying structures. And there is
evidence from circuits that simulations can work slightly better than
physical circuit labs. This was reported in the free online APS PER
journal.

The other problem which has been alluded to is that most NTN1 demos target
bodies at rest which students already understand and believe. They hardly
ever target bodies at motion with balanced forces. One can talk about sail
boats, planes, bicycles, cars... having balanced forces, but students do not
see or believe that the forces are balanced. The only demo I know of that
really works is the dueling fans from the ILDs. The only problem is that
one must precisely balance the fans, but that is easily done with a small
rheostat from Radio Shack. Then when the cart is given a push it travels at
a constant velocity, especially if the track is slightly tilted to
counteract friction.

So the chair in truck demo in the video actually shows what students already
believe and has no effect on their understanding of NTN1 or NTN2. It is
certainly amusing, and probably does no harm to students' understanding of
physics.

John M. Clement
Houston, TX