Two major factors allow the disc to fly -- aerodynamic lift and angular momentum.
Aerodynamic lift is the same principle that allows airplanes to fly. Like the airplane
wing, the frisbee's shape creates a low pressure area above it, and a high pressure pocket
below. Since everything moves towards low pressure, the frisbee moves upwards.
The frisbee wouldn't fly, however, if it wasn't spinning. Momentum is conserved, and since
the spinning disk has angular momentum, it will resist changes in its orientation; i.e. it
won't flip over.
Answered by: Aman Ahuja, Physics student, WPI, Mass.
'Science is facts; just as houses are made of stones, so is science made of facts; but a pile of stones is not a house and a collection of facts is not necessarily science.'