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Re: [Phys-l] momentum dissipation?



Let me first comment on the statement

Momentum should be covered in it's entirety before acceleration comes
up (except for a fancy word that means 'Slope of a Velocity Graph').

The way I see it, students should be able to work out any dynamics
problem using Newton's 2nd, Newton's 3rd and the definitions of velocity
and acceleration before they are ever even exposed to momentum and
mechanical energy.


The order of coverage of topics should be dictated by research into how well
the students have understood the physics. At present most of the research
based curricula that show good gain use a fairly conventional sequence and
only reverse momentum and energy to put energy last. However, this does not
mean that momentum first is inferior.

As far as I know momentum first has not been extensively researched. But
there is research which shows that interactions need to be studied before
Newton's laws. So NTN3 comes first. So the way is paved for momentum by
studying interactions after acceleration.

Unfortunately what actually works is not dictated by logic, but by what you
find out from research. Putting momentum before energy is considered
illogical by many physics teachers, yet the research shows that this
sequence works better.

Robert Karplus who was in many ways the founder of PER put interactions
first. So his sequence might be one to consider researching.

Modeling puts position, velocity, acceleration first. But this fits in well
with the philosophy of having the students do labs where they can figure out
the math relationships. Modelers have also been able in some cases to get
normalized gain over 70%. But again, we do not really know if this is the
optimum pathway to understanding. But when you achieve 90% understanding,
you have come close to saturation.

As to problem solving, it is only valuable if students use the concepts.
Traditional problem solving is often just a bag of tricks that students can
not transfer to analogous problems which are slightly different.

So does anyone know of research that validates momentum first in comparison
with traditional kinematics first? It is useless to argue over paths to
understanding that have not been tested for gain.

John M. Clement
Houston, TX