Originally Posted by Kestrel
Lift is generated as long as the plane can move forward. That's where the thrust comes in.
An airplane flies due to the aerodynamic reactions that happen when air passes at high speed over the wing.
When air passes over the wing, it is forced to pass underneath or over top of it. The length of the wing is larger on the top portion, so according to laws of aerodynamics, the air flow becomes faster, to compensate the larger distance to be travelled. This significantly diminishes the pressure of air on the wing; the difference of pressure under and over the wings creates the necessary lift for flight.
on a belt that would not happen because the plane it not actually moving it staying still... the only movement are the wheels.
EDIT quote taken from Wikipidea