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



These questions that Richard Tarana brings to our attention certainly probe students' understanding of proportional reasoning but, as I read them, I am struck with how detached they are from the real world.

Elementary mechanics, with its concepts of momentum and energy and the explanations of what is happening in terms of Newton's three laws, is certainly based in the real world but here, as in many text-book "problems", there is a huge divide between that real world and the what we present to students.

In the problem shown to us here, there is an attempt to link algebraic manipulation wit the real world: a bowling ball, a car, a path and even rain. However the way these real world things are treated take the problems way, way from reality. The momentum of the bowling ball doubles (how?); the kinetic energy of the ball doubles (how?); the radius of the track doubles (how?); the rain immediately halves the coefficient of friction (how?); the mass of the car doubles (how?). All these "hows" are non-trivial. Certainly they all convey to students the message that the physics they are being taught and being examined about has little (nothing?) to do with the real world.

Brian McInnes
Honorary Associate Professor
Sydney University Physics Education Research Group (SUPER)