[QUOTE=r_duff,Dec 2 2005, 05:24 PM] i dunno if this is a good example or not, but:

If you have a helicopter whos blades spin at 2000 rpm clockwise, and it flies into the center of a tornado also spinning at 2000 rpm clockwise, wouldnt the helicopter fall because the blades are not moving relative to the air its supposed to be pushing against??

Same thing with the plane.

 

Really? I thought there wouldn't be enough lift if the plane wasn't moving forward much. Maybe I just don't know how the heck planes work.

 

That's where everyone is misunderstanding this. The plane WILL move forward, because it's prop/jet is creating THRUST...the wheels on the bottom are just along for the ride. It's NOT like a car on a dyno.

 

Let me try coming at it from a different direction.

A plane is coming in to land at 200 mph. It's going to land on a conveyor belt that is moving in the opposite direction at 200 mph. What happens when the plane lands? Does it stop immediately simply because the conveyor belt is there? Absolutely not. The plane lands and rolls down the runway exactly as normal, except the wheels will spin twice as fast.

Does that illustrate the point any better? About the only other thing I can think of to explain more clearly than I have is to break out a scanner, a free-body diagram, and some equations .

 

Oh, you know, I kinda see it.

 

you're assuming the plane needs the conveyor to move forward. Unlike a car, an airplane does NOT need to push against the ground in order to move forward. The conveyer turning does nothing to the plane engine's forward thrust.

Using Newton's third law, it gains forward momentum when it pushes air back through its engine.

 

[QUOTE=r_duff,Dec 2 2005, 06:13 PM] OHHHHHHHHHHHHHHHHHHHHHHHHHHHHH i get it. its a trick question kinda.

 

hot water freezes faster than cold water?

 

Only on a runway!

 

yes boiling water will make ice faster than room temperature water when both placed in freezer. there's a trick however.