So...about that plane on the treadmill...

"Darkwing" theducksmailATyahoo.com wrote in message
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"John T" wrote in message
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"Darkwing" theducksmail"AT"yahoo.com wrote in message


First, the question posed in the link by the OP of this thread is an
incorrect variation of the original. The original problem asks: "A plane
is standing on a giant treadmill. The plane moves in one direction, while
the treadmill moves in the opposite direction and at the same speed as
the plane. Can the plane take off?"

As has been explained, placing a car on the question's treadmill would
result in a stationary vehicle relative to the observer standing beside
the treadmill. The reason is the car derives its propulsion through the
wheels sitting on the treadmill and the speed of the car is measured by
how fast the wheels are turning. The faster the wheels turn, the "faster"
the car moves. However, this is only relative to the treadmill belt. To
the observer standing beside the treadmill, the car is motionless. If the
driver placed his hand out the window, he would feel no wind even though
his "speed" as indicated by the speedometer may be 100 miles per hour.

Hmm. That presumes that "at the same speed as the plane" means "as fast as
necessary to cancel the forward motion." If you take your car analogy and
apply it to the plane, then the treadmill must try to run backwards as fast
as necessary to cancel forward motion - which is, Ah, let's just say
difficult.

To be consistent with your conclusions about the plane's motion, then the
car would also move. Using the object's motion as the defining parameter to
determine the treadmill speed, then a stable state can be reached with
either
1) a plane with forward motion X, treadmill with motion -X, wheels
spinning at 2X, thrust applied to achieve speed X
2) a car with forward motion X, treadmill with motion -X, wheels
spinning at 2X, thrust applied to achieve speed 2X

Accelerate either the plane or the car with X from 0 to, say, 65. The plane
will take off. The car will drive off the end of the treadmill.

John T


Thank you for your reply. Here is my .02, it would seem that the plane
never actually moves in respect to the observer no matter how fast the
treadmill moves, the plane will just take off like it is hovering and then
slowly accelerate away?

I guess I'll have to set this up and try it, I do have a few RC planes
laying around and I have a treadmill so I guess I'll know one way or
another, unless Mythbusters beats me to the punch.

-------------------------------------------------------
DW


DW,

None of the people that believe the plane will fly say that it will fly with
no forward motion. The claim is that the plane will accelerate to flying
speed in spite of the treadmill moving in the opposite direction.