Sometimes, when my students struggle with this, I take them back to the problem of a person standing on an elevator. If the elevator is accelerating upward, they can usually agree that the two forces acting are the normal force of the floor pushing up and the earth pulling down. And usually there is no argument that if the person accelerates upward, the floor force must be the greater of the two. But then I ask: "Since it's accelerating upward, shouldn't we add an 'upwardial force'?" I let them tell me that no such force needs to be added - that is the name of the NET force in the upward direction, the sum of the forces ALREADY ON the free body diagram. Then we go back to the circular examples.
________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Dan Crowe [Dan.Crowe@Loudoun.K12.VA.US]
Sent: Sunday, September 23, 2007 3:43 PM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] [ap-physics] The Swinging Bucket Problem
I regularly use the longer, but more precise, phrase "the sum of the
forces in the centripetal direction".
Daniel Crowe
Loudoun Academy of Science
dan.crowe@loudoun.k12.va.us
korsunskyb@mail.weston.org 09/23/07 1:59 PM >>>
... which is just another argument for banishing the expression
"centripetal force" from the English language...
:-)
Boris Korsunsky, EdD
Physics Teacher
Weston High School
voice 781-529-8030 x 7609
korsunbo@post.harvard.edu
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