Date: Dec 26, 2012 10:25 PM
Author: Peter Duveen
Subject: Re: Physics problem --ball rolling down an inclined plane

Well, Kirby, nice to know people are paying attention to the issue. Regarding the first link, 

"If you "race" these objects down the incline, they would definitely not tie! This is because Newton's Second Law for Rotation says that the rotational acceleration of an object equals the net torque on the object divided by its rotational inertia. (Net torque replaces net force, and rotational inertia replaces mass in "regular" Newton's Second Law.)"

My sense in reading Newton's Principia is that he wanted to steer clear of rotational problems. "Newton's Second Law for Rotation" I dare say did not exist. This is one problem with a very common approach to the teaching of mechanics. It is first promised that Newton's laws will explain everything, and then there is a switch and bait, an introduction of new principles, such as torque, etc. that are really not derivable from the first three laws, or at least no derivation is given, if one is indeed possible. In fact, the principle of conservation of energy is also an extraneous principle not included in Newton's tool kit. You don't think this is confusing to students? It certainly got me confused back then.