Originally posted by st00p1dfac3
This is why I didn't actually post the question again, however, if it helps I'll post a very specific version of the question which leaves no argument about what it means. If I do that, it also answers the question for anyone brighter than a burnt-out light bulb. That, of course, didn't help on the other site.
This is posted assuming some of the "knuckleheads" have done highschool level physics.
Ask them to draw you a force vector diagram of the forces acting on the plane.
They should draw a forward force of the propellers thrust, a downward force of gravity on the plane and the reciprocal upward force of the treadmill on the plane (which stops the plane getting pulled through the treadmill to the centre of the earth).
Then you can say to them "See there is a net force acting on the plane, the plane must start moving"
They'll say something like "no the treadmill slows the plane down"
You say "No, the wheels de-couple the plane from the treadmill, no horizontal force can be applied to the plane via unpowered, freewheeling wheels with frictionless bearings".
Hopefully then they'll say "Oh OK, you're right". (But realistically i doubt it, some people just won't listen - they may be capable of understanding what you're saying but they won't try)
Good luck with your sisyphean task