Re: Friction

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

> Lowell,
> I think you've been cheating! It sounds rather like you are dragging a
> 'train' of two or more blocks around, each independently resting on the lab
> table surface.

It was not a train of blocks but the blocks are stacked on top of each 
other.  Then the block is turned on end to change the surface area.  The 
bottom block was wrapped with paper so the same surface material touched 
the lab table.

>  This is inappropriate if true.
>   The general idea is that a bearing surface of widely varying area only
> bears at 3 points.
>  Two independent blocks obviously bear at six points.

It was one independent block touching the table.


>  This would evidently affect the unstick force.
>  Other factors that might vary the three-point bearing idealization are a
> coating of wax or very carefully smoothed bearing surfaces.

The lab table surface is VERY smooth - polished stone.

Lowell