"cjcampbell" wrote

The question goes like this:

"An airplane on a runway sits on a conveyer belt that moves in the
opposite direction at exactly the speed that the airplane is moving
forward. Does the airplane take off?" (Assuming the tires hold out, of
course.)

Cecil Adams (world's smartest human being) says that it will take off
normally.

Maybe he's not so smart after all :)

On a calm day you can run and feel a wind on your face because you are
moving across the ground as well as through the air. But, if you run on a
treadmill there will be no wind because you are not moving through the air -
the air is calm so it has no relative motion with respect to the ground.
Neither do you when you run on a treadmill.

Assume the airplane is on the conveyor and there is a 10 kt headwind, and
assume we need 60 kts for takeoff. The only way to generate the additional
50 kts of airspeed is by moving across the ground at 50 kts. If the
airplane is standing still because the conveyor is moving backwards at the
same speed that the airplane is moving across the ground at, then the
airspeed will still be 10 kts.

If the conveyor keeps the airplane standing still relative to the ground,
then it cannot take off. If it could, then we'd all have problems during
run up because the brakes do the same thing that the theoretical conveyor
does - prevent motion across the ground.

BDS