Physics question/riddle. This is a good one, read it.

[Arya Ebrahimi]

a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.

the question is

will the plane take off or not?

Well? Will it?

[srafj40]

Into the wind? Or down wind? What is the wind speed on this specific day?

[Arya Ebrahimi]

No wind, it's a calm day.

[rusty_tlc]

The wing depends on air speed for lift, ground speed is meaningless.

[LoveTractor]

ditto

EDITTED 4/6/07 TO HELP THOSE JUST STARTING TO READ THIS THREAD
THE PLANE FLIES!

The reason I do this is because many here(including myself) are turning into broken records trying to convince newbs just starting to wrap their squash around the idea that the plane does indeed fly. This thread gets brought up every few months with someone trying to make an argument that the plane does not take off. This is an attempt to nip it in the bud early. If you STILL feel you have an argument that the plane does not fly, have at it...but it's the same wrong argument over and over again. And it's wrong. I too once thought the plane did not fly, but finally saw the light. The plane flies. Period.


The evolution of my proof:

Originally Posted by LoveTractor

.....
The conveyor belt is irrelevant. The wheels are, for the most part, free-spinning. The engine/prop/jet will eventually produce the critical amount ot force to put the plane into "flight."
I have an awful example I came up with, but I understand it.
Let's say the Earth rotates at X speed along the equator east to west. A plane travels just above the equator at X speed along the equator west to east. Is the plane flying? Yes. If the plane (theoretically) lands along the equator on its "free-spinning" wheels, does it just stand still? No. The wheels are just spinning at 2X speed. If the plane pulls up, is it flying again? Yes. Sort of a grandiose example, but the best I could come up with.

Originally Posted by LoveTractor

With a bike, the wheels are used to push force onto the ground to propel it. Same concept as walking/running(feet), cars(tires/accelerator), canoes(paddle/water), skis on a flat surface(poles). Planes don't need the ground to exert force to propel it. The engines of a plane uses air to propel it. Hence the ground/wheels/conveyor belt is irrelevant. The plane's engine(s)/prop(s) will at some point exert enough force against the air behind the plane to propel it into flight.
You feelin' it yet?

Originally Posted by LoveTractor

Here. Maybe my POS force diagram(see below) will help.
The force of the conveyor belt is null since it just spins the wheels. All those who think the force of the conveyor belt is somehow "stopping" the plane are mistaken. The force of the conveyor belts is ONLY spinning the wheels causeing NO drag on the plane. There is no drag on the plane at all. The force from the engines pushing backwards causes the plane to thrust forward into flight.

Originally Posted by LoveTractor

(see diagram below)
F(of the conveyor belt)=m(conveyor surface pressing wheels)a(speed conveyor belt is traveling) is meaningless in this problem since it's just spinning the wheels. It is ONLY spinning the wheels and doing nothing to hinder the F(of the engine thrust)=m(air behind plane)a(engine thrust backwards).
F(of the engine thrust)=m(air behind plane)a(engine thrust backwards) causes the plane to thrust forward and into flight.
The force of the conveyor belt could be many times that of the plane's engine force and it wouldn't do a damn thing to produce drag and stop the plane from flying.

At least I think that's the right physics. I get it.

Originally Posted by LoveTractor

Oh goody. I get to post my solution for a fifth time.

The point is that the force of the conveyor belt is irrelevant. The conveyor belt could be going a gazillion times faster than the plane and it still wouldn't produce drag since the force of the conveyor belt just goes up and around the plane's free-spinning wheels. No drag=flight.

sheesh

And just for posterity...
Right now.
yes:90
no:163

Originally Posted by LoveTractor

The ONLY thing that can "stop" a plane(or put force on the front of the plane)is drag. Show me where there is ANY drag being produced. I've already shown everyone with a physics force diagram just a few posts back that there is ABSO-FUCKIN-LUTELY no drag being produced. Not by the conveyor belt since the conveyor belt force that you THINK is producing drag is only going under the free-spinning wheel, up the back of the free-spinning wheel, and right back out the front of the free-spinning wheel. And there is no drag being produced from anywhere else. NO DRAG=THE PLANE THRUSTS FORWARD INTO FLIGHT.


Again, I ask: Where the hell do you see drag being produced? Because drag is the only force stopping ANY plane from flying. The conveyor belt(for the 50 billionth time ) does not produce drag.

Originally Posted by LoveTractor

As I've said before Johnny(although you ignore me), if the plane is going 200mph and the conveyor is going 10,000,000mph, the plane still takes off. Although the FREE-SPINNING wheels would be going 10,000,200mph. But the 10,00,200mph FREE-SPINNING wheels are not producing ANY drag since they are...(wait for it...wait for it)...FREE-SPINNING.

Now, I'll admit that they have to be some pretty, pretty, pretty well-lubricated wheels.

A physics force diagram showing the forces involved in the problem:

[Arya Ebrahimi]

FYI, I'm in agreement that it will take off, but apparently this question has spawned 500+ reply posts on other forums

Oh, and for those of you voting no, I wanna hear your reasoning!

[srafj40]

Originally Posted by rusty_tlc

The wing depends on air speed for lift, ground speed is meaningless.

Treating it as a linear thinking problem.

Maybe, just maybe, it was in the gulf coast region as winds picked up to a Cat. 4 or so.

Then again, I am not all that smart.

[expat]

If the plane is a jet, there is no apparent wind, therefore no lift... If the plane is a prop job, there may be some wind blown across the wings generating some lift, but not likely enough to take off. My opinion...

Now, if you had a Landcruiser on the same runway, and you stuck your hand out the window, you wouldn't feel anything, as long as there is no frictional wind dragged along the same runway.

[Lashcat]

Yes it will take off. Planes gain lift from air speed not ground speed. The prop would still move the plane forward due to the thrust produced by the prop. The speed of the convayor would only make the wheels thurn faster. If this were to be a real life situation i would hate to be the pilot tring it due to the fact of trying to control the plane until it gained enough speed to gian flight. Too much brake on either pedal would end up in a bad situation.

[baxter650]

Yes it will, if the plane is going say 200 knots forward the belt will be going 200knots backward. The plane still has forward speed and will take off, the wheels will be going like hell at 400 knots though.

[Hawke]

No go. Plane stationary.

[Red Herring]

I think if the conveyor belt is preventing any forward motion of the plane by keeping its relative ground speed at 0, then no lift off will occur. Regardless of thrust applied, if the conveyor belt is matching the speed of the plane in the opposite direction, the plane could not generate speed or thus lift, regardless of how much air was passing through the engines. Ground speed is needed for initial take off.

[srafj40]

Originally Posted by baxter650

Yes it will, if the plane is going say 200 knots forward the belt will be going 200knots backward. The plane still has forward speed and will take off, the wheels will be going like hell at 400 knots though.

Sorry but last time I checked a planes engine does not drive the wheels.

[LoveTractor]

In order for flight to occur, enough wind must hit the front of the wing so that lift occurs under the wing and therefore causing flight. If the plane is on a conveyor belt that is moving backwards and only the wheels are moving, there is no wind on the front of the wing at all to cause lift. Therefore no flight.

What did I win?

Crap I'm a slow typer.

[srafj40]

Originally Posted by Hawke

No go. Plane stationary.

What he said.

[MoJ]

Originally Posted by LoveTractor

In order for flight to occur, enough wind must hit the front of the wing so that lift occurs under the wing and therefore causing flight. If the plane is on a conveyor belt that is moving backwards and only the wheels are moving, there is no wind on the front of the wing at all to cause lift. Therefore no flight.

What did I win?

Crap I'm a slow typer.

+1

Gotsta have the flow.

[Arya Ebrahimi]

The wheels on an airplane are free spinning. They are not driven. Therefore it is irrelevant what speed the ground is moving at, it is only relevant what speed the plane is moving in relation to the rest of the earth.

In short, I concur w/ Baxter650

[Red Herring]

Originally Posted by Lashcat

Yes it will take off. Planes gain lift from air speed not ground speed. The prop would still move the plane forward due to the thrust produced by the prop. The speed of the convayor would only make the wheels thurn faster. If this were to be a real life situation i would hate to be the pilot tring it due to the fact of trying to control the plane until it gained enough speed to gian flight. Too much brake on either pedal would end up in a bad situation.

I said no initially, but I think I am coming round to your camp! I think your right. It would be different if the engines drove the wheels.

[rusty_tlc]

Originally Posted by baxter650

Yes it will, if the plane is going say 200 knots forward the belt will be going 200knots backward. The plane still has forward speed and will take off, the wheels will be going like hell at 400 knots though.

If the plane is exerting forward thrust equivelent to 200 knots and the belt is moving backward at 200 knots the net air speed will be zero.

[LoveTractor]

Originally Posted by Arya Ebrahimi

the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction

=no wind on front of wing to cause lift. The plane will not move forward because of this conveyor belt system. A plane's engines move the plane forward(without wicked conveyor system) which causes wind on front of wing which causes lift which causes flight. No move forward=no lift=no flight.

[Arya Ebrahimi]

Originally Posted by LoveTractor

=no wind on front of wing to cause lift. The plane will not move forward because of this system. A plane's engines move the plane forward which causes wind on front of wing which causes lift which causes lift. No move forward=no lift=no flight.

The plane is moving at 200 knots forward in relation to the ground. This sets the track in motion at 200 knots backwards. The plane is STILL moving forward at 200 knots which means air over the wings. The wheels of the plane, however, are spinning at 400 knots.

[Lashcat]

If the wheels were what caused the plan to gain speed I would agree with those of you who say no. again a plane gians speed no matter if it is on the ground or in the air by the amount of air the the prop is able to push. The plane is pulled along but the air the props process. So how can the convayor negate the amount of thrust produced by the prop.

If you can explain that to me i will be glad to put on a pointed hat and sit in the corner.

[rusty_tlc]

Originally Posted by LoveTractor

In order for flight to occur, enough wind must hit the front of the wing so that lift occurs under the wing and therefore causing flight. If the plane is on a conveyor belt that is moving backwards and only the wheels are moving, there is no wind on the front of the wing at all to cause lift. Therefore no flight.

What did I win?

Crap I'm a slow typer.

Actually lift is generated because the top surface of the wing is longer than the bottom surface. The air crossing the top moves faster and this creates low pressure which in turn generates lift.

[White Shark]

Low air pressure due to air flow over the greater surface area on top of the wing generates lift. No air flow over the wings = no lift. A prop plane will provide forward motion, but if the ground moves and negates forward motion, then the props are generating nothing but prop wash and sufficient lift will not occur to get the plane off the ground.

The question states that the conveyor matches the forward motion. That would case a stasis to occur where the plane is at full throttle and is still maintaining the original position. Thus, no air flow over the wings other than prop wash, and the jet turbines throw thrust behind the wings.

[sisukid1975]

Yeah, I screwed up and didn't think it through all the way....

It will take off....

Newtons third law....

The plane does not depend on traction to the ground for it's motion. It's engines will provide thrust since they are pumping air, whose movemnet is not relative to the ground, but independant of it.

So yeah, if the plane will move, but the wheels will spin twice as fast.

Fred