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[Phys-L] Re: Quick question on static frictionHi All

I thought purists objected to this use of "flow" in teaching because it
obscured the "actual" mechanisms, or confused the students. But its use
by the cognoscenti (among themselves) was OK because it was an
enlightened reality, as opposed to the students' naive reality.


Brian Whatcott wrote:

At 11:10 PM 3/11/2005, Bob L., you wrote:

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?

I find it helpful to recall that a force applied through a distance in the
direction in which the force is applied, does work.
While a force applied through a distance opposite the direction of the
force, has work done to it - which is conveniently called a negative force
from the view of the entity applying the force.
This leads to a vivid illustration of the transmission of work, through a
chain to an object to be dragged, say. This balance sheet is easily
described as "energy flow" through the chain, to the fury of purists, it is

Brian Whatcott Altus OK Eureka!

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