hmmm.... physics question for you guys....

[dg]

Re: hmmm.... physics question for you guys....

That is an interesting point. The plane has to overcome inertia to start moving forward, whether it is on a normal runway or on a conveyor. At the very beginning, when the conveyor reads the forward speed of the plane and tries to respond, the plane has to have begun to move for an instant. Inertia has been overcome at that point. It's kind of a chicken-or-the-egg argument, but the way I read it the conveyor has to respond, so movement of the plane occurs an instant before the conveyor counteracts it (or tries to.)

[toejam]

Re: hmmm.... physics question for you guys....

[ QUOTE ]
Why do the wheels on an airplane rotate?

[/ QUOTE ]
They don't... if they're square. [img]/images/graemlins/laugh.gif[/img]

[Newc]

Re: hmmm.... physics question for you guys....

Let me take this opportunity to make a few things crystal clear:

#1 - If you cannot remain engaged in this discussion without parsing insults, then please do not engage in the discussion at all. This isn't grade school.

#2 - This topic is not important enough to place my very long-standing membership on the line, regardless of who else thinks theirs is. If you think so little of your membership, or of other members, then by all means, you know where the exit is - excuse yourself at any time.

#3 - Please bear a modicum of respect for those who are actively engaged in this discussion by not making dissimilar comparisons or injecting random, inapplicable similies of totally different vehicles or vehicular components.

Thank you.
================================================== ====================

Back to the discussion:

[ QUOTE ]
The wheels turn as a result of the forward movement of the plane.

[/ QUOTE ]

So then you agree that the wheels turn because the thrust of the engines induces forward motion and is transferred kinetically through the plane's physical structure.
I will concede for the sake of clarity that the wheels are being pulled by the plane, rather than the plane being pushed by the wheels.
Is this not correct?

[DumpyWumpy]

Re: hmmm.... physics question for you guys....

Another interesting point...Forgetting about the speed matching conveyor for a second just to throw some ideas out there, if the planes engines are turned off and the conveyor is going -100MPH, then relative to the plane, the air in front of the turbines is going forward at 100MPH. Wouldn't the plane need to exert twice as much force from the turbines in order to suck in the air in front of it that is moving forward at 100MPH to an observer in the plane? It's like if you had a a vaccuum lying on the ground with baseball in front of it, say that the vaccuum was strong enough to suck the ball into the vaccuum. But if the ball is travelling forwards at 100MPH, that same vaccuum is going to have to be MUCH stronger to reverse the direction of that ball and suck it backwards. I am starting to think that the plane wouldn't move just because of this fact.

[dg]

Re: hmmm.... physics question for you guys....

The wheels are along for the ride and in no way propel the plane. If you produce enough thrust, even Joe's square-wheeled plane will fly. [img]/images/graemlins/laugh.gif[/img]

[dg]

Re: hmmm.... physics question for you guys....

[ QUOTE ]
Let me take this opportunity to make a few things crystal clear:

#1 - If you cannot remain engaged in this discussion without parsing insults, then please do not engage in the discussion at all. This isn't grade school.

#2 - This topic is not important enough to place my very long-standing membership on the line, regardless of who else thinks theirs is. If you think so little of your membership, or of other members, then by all means, you know where the exit is - excuse yourself at any time.

#3 - Please bear a modicum of respect for those who are actively engaged in this discussion by not making dissimilar comparisons or injecting random, inapplicable similies of totally different vehicles or vehicular components.

Thank you.
================================================== ====================



[/ QUOTE ]

[img]/images/graemlins/toast.gif[/img]

Great point, & I agree %100. This is a great puzzle & I see that it may be impossible for each of us to explain our perspectives in words well enough to sway others. It's frustrating as hell. [img]/images/graemlins/laugh.gif[/img] No need for any animosity, & I sure don't have any. [img]/images/graemlins/toast.gif[/img]

[hippietim]

Re: hmmm.... physics question for you guys....

Newc, the discussion has jumped the shark.

[dg]

Re: hmmm.... physics question for you guys....

Could the Fonz jump the shark if the ski-boat is running upstream against a current that increases exactly in proportion to the boat's forward speed? I say yes, because the Fonz is actually propelled by mojo.

[LouSiffer]

Re: hmmm.... physics question for you guys....

Well...I am done with this thread. I have stated the plane will gain forward movement. It does not take a quantum physics degree to understand.

The people that still think it will remain stationary, obviously are so enraged with the argument, they have tossed out all reasoning. The example I gave you with a skateboard is exactly the same issue we are discussing, but, on a smaller scale.

I can't help it if I tossed out my offer to leave the forum....it just shows I have more balls and a better understanding of physics than most others. If it would have been a question on quilt making....I never would have tossed that offer up because I know crap about it.-Lou

[GodOfRhythm]

Re: hmmm.... physics question for you guys....

A plane with pontoons won't be able to take off from a conveyor belt either.

The plane will remain completely dependant on its weels until it reaches lift.

A plane without weels, just sliding on its hull might be able to take off ON NORMAL RUNWAYS, if its engines produce enough thrust to overcome the extra friction of the entire hull sliding over the tarmac, yes, indeed, same with pontoons.

BUT the conveyor belt would be moving in the opposite direction, the weels would remain in the same place, eventhough the jets are thrusting it forward, this plane with weels rests on its weels (until it reaches lift). If the plane starts revving up and the jets start exerting more power the weels will remain ESSENTIAL since they are the main points of support and the place where gravity is counteracted (again; UNTIL THE PLANE REACHES LIFT), now the conveyor belt revvs up 100% EQUALLY to whatever forward thrust and speed the plane is reaching.

Nothing will happen, since the weels will still be on the conveyor belt and the conveyor belt is going in the opposite way.

If the conveyor belt was anti-slip the plane would be rolling over its weels.

If the conveyor belt was slick and smooth, the weels would be partially turning, partially 'skiing' on the exact same location.

This is the paradox, for the plane to take off it needs to reach lift, but it is 100% reliant on its weels/pontoons/ski's/hull whatever until it REACHES SUFFICIENT airflow over and under the wings to achieve the required lift but it can not reach the lift so it stays dependant on its weels, so it stays on one place on the conveyor belt so it doesn't reach lift so it stays dependant on its weels so it stays on the same place on the conveyor belt so it does not reach airflow so it does not reach lift so it stays dependant on its weels... ad infinitum.

As long as the conveyor belt keeps matchin the speed of the plane perfectly there is NO WAY the plane will move forward.

--------

And Xeno to come back to your argument, the weels would indeed start spinning faster and faster since the plane is exerting more thrust and the conveyor belt is actively and immediatly counteracting the increase in thrust with its own increase of movement in the other direction.

This could go on endlessly until the weels, the ballbearings or the entire landinggear reaches a point of critical speed and then they would just collapse or the tires would explode, causing the plane to dive onto the conveyor belt and the plane would be catapulted away violently and break up / explode.

[DumpyWumpy]

Re: hmmm.... physics question for you guys....

Yeah I am pretty much positive that plane is goin' nowhere boys...

[Bert]

Re: hmmm.... physics question for you guys....

[ QUOTE ]
So if the conveyor is moving at 100MPH FORWARD, and the plane turns on the engines and cranks it to 100MPH in the SAME DIRECTION,

[/ QUOTE ]

First of all plane engines don't have speed settings. They can be set to generate a particular amount of thrust, which translates into forward force. This force generates either acceleration, or it can be set low enough to simply counteract existing forward forces such as wind friction to maintain current velocity.

[ QUOTE ]
...you are saying that the planes wheels will not turn at all and that the plane will go 100MPH forward, because the wheels have nothing to do with it. But in this case, the plane is going 100MPH forward with the engines turned off also. So what the hell do you think of that boys? If you say that the conveyor moving in the same direction is going to support the motion of the plane and increase it at all, then you are TOTALLY contradicting your arguement that the plane will move forward even when the conveyor is going in the opposite direction.

[/ QUOTE ]

I'm not sure what you're getting at.

[ QUOTE ]
So if the plane has it's engines turned off, and the conveyor starts going 100MPH forward, the plane will move along with the conveyor at 100MPH, this is guaranteed.

[/ QUOTE ]

Guaranteed how? The plane has frictional forces pushing it back (wind) and some pushing it forward (the conveyor+wheel and wheel bearing friction). At some point, the wind induced force will overcome the weak frictional wheel forces, which will prevent the plane from going any faster. A plane's wings with flaps in the down position generate a lot of resistance, and you can be VERY sure that without *any* engine power, a conveyer belt alone would not get the plane going 100MPH unless you make (even more) ridiculous assumptions, like the plane's wheels are glued to the conveyer or there is a hefty tail wind.

[GodOfRhythm]

Re: hmmm.... physics question for you guys....

Actually xeno, if the tires DO break up and with a bit of 'chance' the plane might be pelted into the air by the violent break up of the landing gear, if the engines were revving at full speed, it would become momentarily independant from the weels (since the upward force from the violent breakup is making it jump into the air, exerting greater force than gravity) if the engines were revving hard enough and the leap was high enough it could actually move abit forward, but crashing would still be the final result. (unless it were a VERY light plane with a VERY LIGHT BUT POWERFUL ENGINE)

[Bert]

Re: hmmm.... physics question for you guys....

[ QUOTE ]
And Xeno to come back to your argument, the weels would indeed start spinning faster and faster since the plane is exerting more thrust and the conveyor belt is actively and immediatly counteracting the increase in thrust with its own increase of movement in the other direction.

This could go on endlessly until the weels, the ballbearings or the entire landinggear reaches a point of critical speed and then they would just collapse or the tires would explode, causing the plane to dive onto the conveyor belt and the plane would be catapulted away violently and break up / explode.

[/ QUOTE ]

GOR -- look how the original problem is stated. The conveyer belt moves the exact same speed as the plane, only in the opposite direction. Thus, for the conveyer belt to be going 200 MPH backwards implies the plane is already travelling 200 MPH forwards relative to the ground & air. This is plenty of speed to achieve lift, resulting in flying. The wheels in this case turn at a rate equivalent to 400 MPH on non-moving ground. There is no scenario in which the wheels would speed up endlessly.

[Endrik]

Re: hmmm.... physics question for you guys....

Bert, there is no air/wind wich is the thing that makes the plane fly.