Re: Relative velocity problem....

[herbgottlieb@juno.com]

  Maurice Barnhill <mvb@UDel.Edu> writes:
> Since my post,  "Surendranath Reddy.B." <bsreddy@hd1.vsnl.net.in> has
> described a demo that I like better than mine.  However, I checked 
> mine with a steel ball from the demo room and with chalk; the steel ball
> worked, but on some trials the chalk stopped dead on the table, so I
> guess that chalk or marble could easily go backward.  

The trouble with balls, marbles or a stick of chalk is that they incur a
rotary acceleration so they will continue to roll backwards after they
leave the bottom
of the forward-moving incline.

Another idea is to use a slow- moving battery-operated toy (such as a
bulldozer)
on a LONG board.  Start the toy on the board moving to the left  while a
student pulls the entire board at a comparatively fast rate to the right
.. Although the bulldozer is moving to the left with respect to the board,
it is moving reight with respect to the table.

Herb Gottlieb from New York City 
(Where we still have some toy  bulldozers that work from the old Project
Physics Days.)