Re: Chain Problem.

[Lowell Herr <herr@catseq.catlin.edu>]

Rick,

See prior post.  This is why I only collect data while the chain is in 
contact with the Smart Pulley.  So long as the pulley is rotating, the 
student can collect useful data.  The effect you describe is still 
present but increasing acceleration can be measured so long as there is 
contact between the falling chain and the pulley.

My main problem with the experiment deals with the friction between the 
chain and the aluminum PASCO track.  I don't think it is possible to 
match theory with experimental evidence but we can discuss why there is 
a difference between the two.  These PHYS-L discussions will give me lots to 
think about and discuss with my students when we do this experiment 
again.

Lowell

 On Fri, 10 Oct 1997, Richard W. Tarara wrote:

> In the idealized problem the rope/chain falls straight down, but if it is
> moving horizontally just before leaving the table, then there must be a
> horizontal force that opposes that motion just as the chain leaves the
> table.  That force must increase with time since the horizontal momentum of
> each chain segment increases with time (or as we get near the end of the
> chain) and the time period in which the chain segment must change its
> motion from horizontal to vertical is decreasing.  This is certainly a
> problem that one does not want to look at too closely--at least not until
> graduate school!
>
> Rick
> ----------
> > From: Leigh Palmer <palmer@sfu.ca>
>
>
> > To see that the horizontal component is present (Donald knows
> > this already, which is why he suggested the frictionless tube
> > in the first place) one need merely consider what the rope is
> > doing at the midpoint of its slide off the table. The portion
> > of the rope which is still on the tabletop will be moving
> > horizontally, thust the rope has a horizontal component of
> > momentum. It is easy to see, then, that there must have been
> > a horizontal force acting on the rope.