Re: Laithwaite/Dawson Paper
Gerald O'Docharty ( (no email) )
Tue, 02 Jun 1998 19:00:46 -0400
Fred, greetings!
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.
Regards,
Gerald O'
Fred Epps wrote:
snip:
> Now take the same pendulum and make it horizontal. Put springs on each side
> so that it doesn't need gravity to store the energy of the swing. Put it
> with the bob facing forward on a little cart that is constrained so that it
> can't move from side to side, only backward and forward. Now get the
> pendulum going. All the 'centrifugal force' is in one direction-- forward.
> Does the cart move forward along the track? And what happens to the energy
> stored in the springs?
> I did a little experiment along these lines, and there was no forward
> movement, but the bob wasn't heavy enough to develop much centrifugal
> force, so I guess the question is still open.
>
> Fred