Pedantic moment: 

y=1/x is not a parabola, but is a hyperbola. A parabola looks roughly U shaped
and has no asymptotes.

If you are using ball bearings, rather than coins, the exact shape doesn't much
matter, as long as it has smooth transitions in curvature. You can bend a spline
as a guide in shaping and it will be fine.

As a historical note, back when I was but a wee lad, and in school, we would
mount rubber sheets in  what was basically an embroidery frame and push and pull
points up and down to form hills and valleys. Dropping bb's, or similar small
metal balls, randomly on the surface would give a good approximation of what
electrons in a tube would do. Of course, I am young enough that tubes were
already out, but it was still part of one course and lab.

We had no end of fun tossing a bb tangentially to get the orbits like you are
making up.

whooosh, whooosh, whooosh, whoosh, whoosh, whosh, whsh, whsh, whsh, wsh, wsh,
wsh, wsh, whs, sss, ss, ss, ss, s, s, ziiiiiip




*** This message was sent from a convenience email service, and the reply
address(es) may not match the originating address