I'm confused by this response. Again, I would ask - if I use my hand instead
of the sheet of paper to move the cup - are you saying my hand does no work
to accelerate the cup? My hand still moves with the center of mass. What
makes the paper different?
-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu] On
Behalf Of Aaron Titus
Sent: Friday, March 11, 2005 6:28 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Quick question on static frictionHi All
(F_grav+F_paper) dot Delta r_cm = Delta K_cm
But since the gravitational force is perpendicular to the
center-of-mass displacement, then
F_paper dot Delta r_cm = Delta K_cm
While this equation alone may look like the work done by paper, it is
not. It is in fact the work done by the net force acting through the
center of mass displacement.
Chabay's and Sherwood's textbook teaches application of conservation of
energy to the "real system" and the "point particle system" more
clearly than any book I've ever seen. This was a major reason for me to
adopt their book.
Aaron
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What happened to the vertical contact force of the paper on the cup?