think about this...

[Patrick del Poker Grande]

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Tell me if this analogy makes sense:

I've got my daughter in a stroller going the wrong way on the moving walkway at the airport. I'm standing next to it on the ground, not on the walkway. I reach over and push the stroller hard enough that it moves forward relative to me. If the stroller had wings, there'd be lift. But at this point aren't the wheels moving faster than the walkway? Is this whole thing semantical?

[/ QUOTE ]
This is a good analogy. Go look at kevyk's post and you might be able to reconcile this.

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Tell me if this analogy makes sense:

[/ QUOTE ]
yes

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Is this whole thing semantical?

[/ QUOTE ]

nope.

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hey, i dont post here often, but i do read OOT a bit, but this is the dumbest question ever; im the guy NLSoldier has a bet with.....i need a way to settle this bet......if anyone can help me out with this, it would be greatly appreciated; ive tried to explain the concept of lift, but he just doesnt get it

the only way a plane gets into the air is because of lift; its the only way....to get lift, you need wind over a wing, in this case there is wind, so no lift, so no takeoff

im an aerospace engineering student, and he wont take mine or anyone of my aerospace's buddies answer; please help me settle this! i got $400 on it

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If it helps, I'm not sure NLSoldier is right, but you're wrong.

[/ QUOTE ]

Dear god I hope you are not a practicing rocket scientist

[tolbiny]

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The problem with this scenario is that the drive isn't created by the wheels, so this belt wouldn't result in the plane not moving, it would mean the wheels would be moving REALLY quickly, but the thrust would still push teh plane forward.

This scenario is impossible.

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Yeah, the exact speed I think will be determined by the friction in the axels given that the wheels are not skidding in any way.

[/ QUOTE ]

I was thinking about this earlier, too. I think the wheel speed/conveyor speed would basically accelerate exponentially until the plane took off. Clearly this whole scenario is probably not physically possible, but it's an interesting theory to discuss.

[/ QUOTE ]

Wait- How much money do we have in the crimson challenge fund? Lets give it a go!!!

Subject line = my accredidation

To answer Daryn's question:
Let the system be the fan/board/block. There are no net external forces acting on the system. Thus, the system doesn't move. If you don't like that answer, then look at it a little more microscopically: The fan exerts a force on the air towards the left. By Newton's third law, the air exerts the same force on the fan to the right. The fan force pushes the block to the left with the same force. So the block pushes the skateboard to the left with some force, and the fan pushes the skateboard to the right with the same force (by friction) and the skateboard doesn't move. If htere's no friction, the skateboard will still not move, but the block will move to the left with some acceleration, and the fan will move to the right with some acceleration. The relative amount of acceleration depends on the relative masses of the block and fan- whichever has more mass, accelerates less.

For the plane example, if the belt is moving at some velocity v, then it appears to an observer stationed on the wheel of the plane that the plane is moving at a velocity equal to 2v *relative to the belt*. However, lift is generated by velocity of the air over the wing. The air is not attached to the belt, so the the observer on the wheel sees a velocity of 0 *relative to the air* and thus there is no lift. For those people confused about the two different relative velocities, think about driving a car- you don't think that the passenger is moving relative to you, but you're moving relative to the road.

[Patrick del Poker Grande]

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You realize that in your OP, wheel speed = anything, plane speed = 0.

Obv, if the plane isn't moving forward relative to the air, it doesn't take off.



Unless, of course, your plan was to phrase a question with a clear answer, then try to confuse people so you would have a big thread.

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I've said this multiple times now - at no point in this thread did I say plane speed = zero.

I suggest following Patrick's advice and creating a FBD.

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UHHHHHHHHHHH what is your point.

Either the conveyor belt is moving exactly opposite of the plane or it is not.

HOW is the plane moving? I would love to know, so I can throw my engineering degree in the trash.

[/ QUOTE ]
This is a plane, not a car.

[NLSoldier]

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hey, i dont post here often, but i do read OOT a bit, but this is the dumbest question ever; im the guy NLSoldier has a bet with.....i need a way to settle this bet......if anyone can help me out with this, it would be greatly appreciated; ive tried to explain the concept of lift, but he just doesnt get it

the only way a plane gets into the air is because of lift; its the only way....to get lift, you need wind over a wing, in this case there is wind, so no lift, so no takeoff

im an aerospace engineering student, and he wont take mine or anyone of my aerospace's buddies answer; please help me settle this! i got $400 on it

[/ QUOTE ]
If it helps, I'm not sure NLSoldier is right, but you're wrong.

[/ QUOTE ]

after a brief convo on AIM, i have deduced that NLsoldier wins $400

[/ QUOTE ]

this n00b doesnt realize that you guys are smarter than him. any ideas of sources we could use as proof?

[mmbt0ne]

Ok, I think this will help some people. The numbers aren't really forces, and it's really confusing, but I didn't feel like painting out the explanation on a laptop. Basically, the plane is still moving along the conveyer belt. Think of the engines like a rope pulling the plane.

[Eurotrash]

edit: nevermind

[daryn]

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Let the system be the fan/board/block. There are no net external forces acting on the system. Thus, the system doesn't move.

[/ QUOTE ]


my, that was easy. go umass!