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#24
03-05-2006, 09:52 AM
 enipla Member Join Date: Jul 2001 Location: Colorado Rockies. Posts: 11,887
Quote:
Originally Posted by enipla
How about this? Would it be possible for a plane to take off with a 100mph tail wind? Same thing. Not something anyone would dare to do, but something that would be about as easy as building the hypothetical treadmill.

Quote:
 Originally Posted by paridoxic ground speed? DOH! This is what happens when you consider this as a thought experiment and not a physics equation. What if I've got a 100mph tail wind?
As you can see, I’ve already taken that into account. I’m looking at this as a physics question. The people that don’t believe the plane will take off (BF#2) see this as a thought experiment.

Quote:
 Originally Posted by paridoxic Force generated by the treadmill in the opposite direction (how about a treadmill driven by the same engines as the plane uses?)
Perfect. See below.
Quote:
 Originally Posted by enipla Originally Posted by enipla No. It’s nearly a perfect analogy.
Quote:
 Originally Posted by zut No it's not, really. Changing the treadmill from one that reacts to the plane wheel speed to a simple constant-speed treadmill is changing the meaning of the question.
Where does the question state ‘Wheel Speed’?
Quote:
 Originally Posted by ”The Question” This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same.
bolding mine
Sorry, but you’re the one changing the question.

And in my analogy, I assumed that it was understood that as the toy car speed up, so would the treadmill. Still works.

To expand on my example of a toy car pulled down the runway……

Lets say the treadmill has rollers 6” in diameter. Attach a string from the toy car to a pully the exact same diameter, that is fastened to the ground. When we turn the pully, the toy car moves forward.

Now. Connect that pully to the 6” roller of the tread mill. But cross the belt that connects them. As the pully move clockwise, the roller moves counter clockwise.

Now, crank on the pully. It pulls the car forward. It moves the treadmill backward at the same speed the car is moving forward.

I don’t like this analogy as much as the person pulling the string, since this is a closed system. And the real world stuff would be two closed systems.