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Started by John Mallinckrodt
Mon, 15 May 1995 00:00
Re: Forces
Author: John Mallinckrodt
Date: Mon, 15 May 1995 00:00
Date: Mon, 15 May 1995 00:00
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Guntbert Reiter writes: >Imagine the impact resulted in pure >movement without rotation. More exactly spoken: the result would >be a linear acceleration of the CM. By Newton's laws (inertia...) >we know that from this acceleration the CM should "feel" (I just >can't remember the correct term) a corresponding force pointing >in the opposite direction. So these two forces build a couple and >produce a torque. Guntbert, Imagine all you want, but you've got a powerful adversary in the form of Newton's Laws. (Do some of us really imagine that one could tap on the end of a freely mobile, originally stationary pencil in a direction perpendicular to its length and find that the result of the tap is pure translation?) You are apparently appealing to the "inertial force" that arises in the (briefly) accelerating frame of the object's CM. I happen to be a fan of inertial forces and you are right that the couple produced by the impact and the equal and opposite inertial force explains the rotation observed in the accelerating frame. (It also explains the LACK of acceleration observed in the acceleratING frame.) But you STILL need to account for the rotation that is observed in the inertial frame and there IS only one force in that frame. Fortunately, and not surprisingly, Newton's laws predict this result. John John Mallinckrodt Cal Poly Pomona ajmallinckro@csupomona.edu
Re: Forces
Author: Guntbert Reiter
Date: Thu, 18 May 1995 00:00
Date: Thu, 18 May 1995 00:00
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John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU> wrote: >Imagine all you want, but you've got a powerful adversary in the >form of Newton's Laws. (Do some of us really imagine that one >could tap on the end of a freely mobile, originally stationary >pencil in a direction perpendicular to its length and find that >the result of the tap is pure translation?) Well, I dont. >But you STILL need to account for the >rotation that is observed in the inertial frame and there IS only >one force in that frame. OK. I give in. Part of my statements were a result of unconsciously carrying a *static* concept into a dynamic problem. Guntbert ------------------------------------------------ Guntbert Reiter : guntbert@borg-6.borg-graz.ac.at HTL Weiz Graz Austria
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