Re: [Phys-L] proportional reasoning, scaling laws, et cetera

[Brian McInnes <bmcinnes@pnc.com.au>]

Bill Nettles wrote
>   Instead of "the mass of the car doubles" we could say 2 cars, one  
> with twice the mass of the other, etc.

The situation described is a car travelling around a circular track.   
In the original formulation its mass magically doubles; your  
alternative replaces the car by two cars but that surely in a  
different problem or, rather, the original problem done twice.

You say it's a matter of discerning what is important not in solving a  
problem.  I say that it is important that the problems we present to  
the students are grounded in the real world where momenta, kinetic  
energies, masses and track radii don't change by magic.  Problems in  
physics should be real problems and not mathematical manipulations.