> When the horizontal 'pendulum' swings past the apex or center of its
> arc, the
> center of mass begins to accelerate with a vector component opposite to
> the direction of the centrifugal force vector at the apex. It then gives
> up this momentum as a 'rearward' force when it is stopped by the spring.
> So the net force vector is still zero over a full cycle. Think of an
> extreme where the pendulum goes through a full 180 deg of arc with stops
> at the ends of the arc. When the pendulum hits the stop 100% of its
> momentum is going in the opposite direction of the direction in which
> you got maximum centrifugal force at the center of the arc. With a
> shorter arc it still cancels but the forces are smaller. If you
> integrate all the force vectors over a cycle you will find that they add
> to zero.
OK, I can see that now, it makes sense, and it fits what I observed.
Thanks for the "vector lesson", Gerald..
I've got another idea that's more related to the precession that Laithwaite
talks about but I want to study it a little more before I put it into
circulation.
Fred