Re: Physics graduate from Daryn\'s alma mater\'s answer
 

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Of course the plane has to be moving relative to the air around it (or the ground if that makes it easier).

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this is it, you need wind over the wings for lift!! a plane cannot get in the air without lift! wtf, i can't believe noone gets this

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Please explain specifically what FORCE is stopping the plane from moving forward (relative to the atmosphere, NOT the conveyor belt).

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isn't the whole premise of this post is that the plane isn't moving?

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oh my freaking god - how many times do i have to say this? NOWHERE in this thread did i say that the plane wasn't moving. you are ASSUMING that the plane isn't moving, and that's why you can't understand the problem.

Re: Physics graduate from Daryn\'s alma mater\'s answer
 

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Of course the plane has to be moving relative to the air around it (or the ground if that makes it easier).

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this is it, you need wind over the wings for lift!! a plane cannot get in the air without lift! wtf, i can't believe noone gets this

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Please explain specifically what FORCE is stopping the plane from moving forward (relative to the atmosphere, NOT the conveyor belt).

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isn't the whole premise of this post is that the plane isn't moving?

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I suggest you start at page one and read the thread over again.

Re: think about this...
 

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It's very much like a float plane taking off from the water (where there's also negligible friction).

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No it is not. It would be like a float plane taking off from a river that is moving at an opposite speed of the floats. WOULD NOT TAKE OFF

To simplify:

1. Plane on a runway. Takes off
2. Plane with locked wheels on ice. Takes off.
3. Plane with locked wheels on runway. Doesn't take off.

Note that #3 is the same problem that OP phrased.

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#3 is nothing like what OP phrased. Explain how the wheels will move at the same speed as the plane in this example.

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i'm curious to know why the wheels have to be locked for the plane to take off on ice

Re: think about this...
 

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It's very much like a float plane taking off from the water (where there's also negligible friction).

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No it is not. It would be like a float plane taking off from a river that is moving at an opposite speed of the floats. WOULD NOT TAKE OFF

To simplify:

1. Plane on a runway. Takes off
2. Plane with locked wheels on ice. Takes off.
3. Plane with locked wheels on runway. Doesn't take off.

Note that #3 is the same problem that OP phrased.

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#3 is nothing like what OP phrased. Explain how the wheels will move at the same speed as the plane in this example.

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i'm curious to know why the wheels have to be locked for the plane to take off on ice

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Because otherwise the wheels would slip on the ice and keep you in the same place daryn!!

Re: Physics graduate from Daryn\'s alma mater\'s answer
 

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Please explain specifically what FORCE is stopping the plane from moving forward (relative to the atmosphere, NOT the conveyor belt).

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That actually cleared it up for me.

Re: think about this...
 

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Alright, kids. I'm going to let you in on a little rocket science secret. Prop planes do not generate lift by blowing air over the wings.

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They don't? Do you mean that they don't make lift by blowing the air themselves, or that the airflow across the wings from whatever source doesn't generate any lift?

As for the OP's question, it looks to me like the plane will take off. If there's zero friction in the wheel bearings, they can't exact any forces tangential to gravity on the plane.

So we have a forward force provided by the thrust and that's it, resulting in forward acceleration. The runway can move at whatever speed it wants, and the wheels will spin faster but they can't apply that force to the plane. In this particular example, the wheels will just spin with twice the angular velocity than they would with a fixed runway.

It's very much like a float plane taking off from the water (where there's also negligible friction).

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I get that. I mean I get how the plane can take off, I just don't get how you can say that the wheels are moving at the same speed as the conveyor. I guess I don't understand what speed means. [img]/images/graemlins/confused.gif[/img]

Re: Physics graduate from Daryn\'s alma mater\'s answer
 

this thread is seriously the bomb.


let's think a little about OP's original statement, that the conveyor belt is moving in the opposite direction as the wheels on the plane.

now imagine the plane is completely turned off, there is 0 thrust from the turbines/props. The conveyor belt is moving backwards at 100 feet/sec. The planes wheels are spinning forwards at the same rate. The plane is standing still, no??

now what happens when you turn on the turbines and start generating forward thrust, WTF do you think the plane is going to do???

Re: think about this...
 

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Because otherwise the wheels would slip on the ice and keep you in the same place daryn!!

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LOL!

Re: think about this...
 

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yeah it def. blew my mind. now give the answer plz? and the answer to daryns skateboard thing too. me and my friend have a bet on both.

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The plane can take off - this has already been established.

For Darryn's - as pictured, the skateboard would go backwards. If it were a perfect sail instead of that board, it would stand still.

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describe a perfect sail

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Apologies if this answer has ben posted ( i haven't gotten that far), but the fan/sail would have to be a closed system.

Re: think about this...
 

wow! you win!