Re: [Phys-l] October Physics Challenge

[Carl Mungan <mungan@usna.edu>]

> Ah you are dealing with the consequences of imputing a particular method
> of holding the small mass and ribbon. You visualize a stretchable ribbon
> (shame on you, this is meant to be a physicist';s ribbon!   :-)   and
> the upward force is I suppose an upslope foce to balance the down slope
> gravity vector.
> For some reason, I imagined a clamp appling a normal force to the small
> mass, so the large block can stretch the ribbon as desired while the
> ramps grow more
> high-pitched, so to speak.... would that resolve the issue?
>
> Brian W

Well, I think that's a valiant effort. But not very stable. There is no friction between the ribbon and the prism. If the clamp provides ONLY a normal force, it will slip sideways and the block is likely to tilt the clamp over (I'm imagining it as consisting of a knife edge clamping down on top of the block) and sneak out. Realistically, I think that the blocks have to be help by a normal force perpendicular to the lower edge face of the block. Like a gate that swings open (sideways or upward) as in a ski race. -Carl