Re: apparent weight

[William Beaty <billb@eskimo.com>]

On Tue, 17 Feb 1998, LUDWIK KOWALSKI wrote:

> Let me defend a naive position. It is a risky busines but what do I have
> to loose? I am saying that a cetrifugal force is real, as far as a bead 
> mounted on a rotating stick is concerned. The stick is horizontal and turns 
> about a vertical axis. Suppose I am that bead and I experience acceleration 
> with respect to the beam on which I am sitting. I am gaining speed while 
> sliding away from the axis of rotation. What is wrong with saying that m*a 
> is the centrifugal force? It is very real in my rotating frame, it can hurt 
> by making me dizzy, etc. 

More ingredients for the stone soup:

I was confused about this before I realized that there are two
"centrifugal forces," and only one of them is real.

One is a pseudoforce "caused" by the non-inertial frame.  For example, if
I ride inside a rotating cylinder and toss a ball around, the ball's
trajectory will be very strange.  It will be influenced by the centrifugal
pseudoforce.  Note that this pseudoforce DOES NOT fling the ball outwards.
It can distort the ball's trajectory until it looks like something drawn
by a spirograph.  It has coriolus components and fugal/petal components,
and does not obey Newton's 3rd.

As I ride inside the rotating cylinder, my back interacts with the inner
surface of the cylinder.  The cylinder pushes me inwards, and I push
outwards on the cylinder.  It's a simple Newtonian force pair.  If I wish
to concentrate only on the centripetal component of this force, while
saying that the centrifugal component is unreal, then I VIOLATE NEWTON'S
THIRD LAW.  Does any physics instructor dare to claim that a surface can
"act upon" an object, but that an object cannot "act upon" a surface?  In
an accelerating elevator, is it proper to say that the elevator's floor
applies a force to the rider, but that the rider does not apply a force to
the elevator's floor?


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