"Michael Ware" wrote in message
. ..

"muff528" wrote in message
news:OW2Ff.179$DV2.5@trnddc07...

.....OR relative to each other? If so, there could be just enough thrust
applied to overcome frictional
forces and the airplane doesn't move relative to the world so airspeed
is
0.

That would have to be either a very underpowered airplane, or wheels with
a
lot of friction.

Yes!..that's why I said "COULD be just enough thrust..." More thrust than is
necessary
to overcome friction would result in the airplane moving forward relative to
the air. Then
it's only a question of how much thrust would be necessary to move the plane
forward fast
enough through the air to overcome gravity :-) A little less thrust would
result in the airplane
going backwards but not as fast as the conveyer. In any case the relative
velocities of the
plane to the conveyer would be equal to observers on either object but NOT
to an observer
standing on dirt.


BUT WAIT!!! .... ANY two objects can be said to be moving (or not) at
equal
speeds relative to each other. A point
on the conveyer belt moving east at 4mph and a jet moving west at 600mph
each have a relative velocity of 604

But there's the trick. A treadmill belt isn't really moving at all, it's
turning.

Again, Yes....but that's why I said "a POINT on the conveyer.." not the
conveyer
system itself.

The trick is that the original question as posted asks a question (will the
plane take off) and gives just enough info
to cause assumptions that aren't specified.

Try this for a brain scrambler. Think about a tire on your car, driving
down
the highway. At the point where the tire contacts the ground, it's speed
is
zero. 180° away, at the top, it is moving forward at twice the speed of
the
car.

Yes, but only for a very brief instant in time. And since velocity is
measured as a function of
time, is that point on the tire really moving at all at that one brief
instant when the measurement
is taken? :-)