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We are having a debate on whether air pressure has a net
effect on a book
at rest on a table top. If it does, is it up or down?
My colleague cited the demo done often to show the
strength of the air
pressure force by placing a stick so one end is under a
sheet of newspaper
with the other extending over the edge of the table. It
is easy to break
the stick with a sharp whack on the unsupported end. This
is ostensibly
because the air pressure on the paper keeps the "under
the paper" end at
rest so the pair of torques snaps the stick.
I am thinking that if this is so that when we calculate
the friction
force, the "air pressure force" should be included in the
normal force.
But we never do that as we think the only forces acting
on the book are
the "normal" and "gravity" forces. I have thought that
the air pressure
manages to apply forces to all sides of the book (of
normal size) equally
(for all practical purposes).
Is this to be my first pubic faux-pas of 2005? How do we
resolve this
debate?
Cheers.
Ken Fox