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leinoffs@SUNYACC.EDU wrote:_______________________________________________
If the end of the stick is struck sharply, wouldn't the effect
of rotational
inertia be prominent? I would think that this effects,
depending on the
characteristics of the stick and newspaper would rival those
of atmospheric
pressure and wind resistance.
1) Yeah. But that's not a big deal. It is proverbial that
no matter what you're doing, you can always do it wrong.
I'm sure that the right whack on the right stick would cause it
to break without
any paper covering the other end.
So don't do it that way.
-- The inertial terms scale like (x dot dot).
-- The dynamic pressure terms scale like (x dot)*(x dot).
... so a prolonged modest acceleration is better than a sharp
blow if you want to demonstrate the aerodynamic effects.
2) Also, it helps to compare an open hoop shape
O
|
to a _paddle_ made by gluing paper to a similar hoop,
rather than just resting paper on some object, the point
being to ensure that the paper is not left behind when
you wave the object around.
There's no need to break anything to make the point;
it suffices to let students wave the two objects
around and observe the forces kinesthetically. The
effect is not small.
3) This is also a good opportunity to make the point that
not every force is the gradient of a potential.