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

[Endrik]

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

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i love the way insults are lobbed around here.

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+1 it's soo funny when people talk shit about each other because of some question...ahaa carry on

[TheSteveMan]

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

Now that I've thought about it, I think the plane would require less work from the jets in order to reach the ground speed needed to take off.
The frictional force between the wheels and the conveyor belt is precisely what causes the wheels to roll.
I can't draw a diagram, but let's say you have the plane moving to the right, the conveyor is rolling so that the surface touching the wheels is going left. As the conveyor moves to the left, a leftward force (the friction) is applied to the bottom of the wheel. This force is perpendicular to the radius from the contact point to the wheel's center. That means the force creates a counter-clockwise torque. So even if there is no thrust from the jets, the wheels would ideally roll so that the axles would move in the opposite direction as the conveyor belt. This would be under the assumption that the wheels are perfectly rigid and the normal force of the conveyor belt on the wheels (the upward force that is equal and opposite to the weight of the plane) acts only at contact points at the bottom of the wheels. This also assumes that the wheels roll without slipping.

In the real world, the wheels will compress a little bit under the weight of the plane, and there will be a contact AREA rather than just a contact point for each one, meaning that some of the force will be dissipated.
To make a long story short, the plane will likely move in the direction that the convyor belt is moving, but not at the full speed of the conveyor belt.

In conclusion, roughly the same thrust will be needed for takeoff as if the plane were on flat ground, but due to likely imperfections it would realistically need a bit more than normal.

I could be terribly wrong on this but this is my view on it based on the knowledge I have gained in physics class.

[sworn_enemy]

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

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i love the way insults are lobbed around here.

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Agreed. I honestly feel this is seriously bringing this forum down. It seems like every other thread has to end up in a pissing match of some sort.

[Endrik]

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

anyway, the plane can take off theoretically....at some point... there isn't said how big is the convoyer belt.... if it is a little bigger than the plane...no way the plane can fly...if it's 2 miles long...well theoretically it can happen...but in the real life things happend differently, there are different rules in theoretical world, micro world and macro world...
No one here hasn't seen a plane on the convoyer belt, so no one knows how the plane really acts.
I belive what I see.

[Endrik]

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

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3) Thrust from the jets are applied... the plane will start moving forward.

4) Since the wheels are not providing movement, only allowing it, they roll effortlessly. THE WHEELS ARE ONLY SUPPORTING THE PLANE, NOT PROPELLING IT LIKE A CAR!

5) Plane moves forward and increases speed, passing it's original starting spot (unless it was tethered to the ground, but as to the original question, no it is not) THE WHEELS ARE SPINNING FURIOUSLY BUT DO NOTHING TO SLOW THE PLANE!


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ahhaa, you said it yourself, THE WHEELS ARE ONLY SUPPORTING THE PLANE and THE WHEELS ARE SPINNING FURIOUSLY BUT DO NOTHING TO SLOW THE PLANE!
well the plane has to exerts extra power/speed to do that but remember that the conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

an extra subject to bitch about and calling others retards [img]/images/graemlins/laugh.gif[/img]

[xenophobe]

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

It doesn't matter how big the treadmill is. If the plane is not phsyically tethered to the ground, or physically held in place, it will still move forward when thrust is applied, regardless of which direction or how fast the wheels may be turning...

[Endrik]

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

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Kiddies, this is not much different than holding a roller skate on a moving treadmill. It will go nowhere if you are holding it down, but if you push it one direction or another, it will follow, REGARDLESS of which direction the treadmill is going.

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let's say that the treadmill works like that convoyer, it reads your speed/power and runs in the oppoiste direction. Now if you push the roller skate to one direction, is it a little harder to do than on the steady ground (where the ground doesn't move)? Is it? I've never done it but I guess it is, even a little bit. And if I'm correct, pushing it forward needs some extra power. But remember the system reads your speed, and it will exactly run at the speed wich is inversely proportional to your strenght wich you are applying to move the skate. Can you move a saket wich is on the treadmill wich runs like a mean motherfucker, let's say 10000 miles per hour in opposite direction [img]/images/graemlins/laugh.gif[/img] Can you?
You need to exert some strenght even if you hold the skate down in one position, if your leg or hand is loose, then the skate will go to the direction where the treadmill's belt is going.

Now the plane can theoretically fly if you can move the roller skate forward on the treadmill wich works EXACTLY against you. The more you push the skate, the faster the treadmill runs. Can someone do it.

[vander]

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

I understand the reasoning behind why the plane is still suppose to take off but I just don't buy it that easily.
Rollerskates and whetever and planes are not similar. All the weight a 747 standing on a runway before taxiing transfers to it's wheels is a lot theorize as inconsequential. I would not want to be a passenger on the plane testing this theory. I'm with Endrik..I'd have to see it to beleive it. [img]/images/graemlins/tongue.gif[/img]

[RobRR]

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

Well then hopefully it will be on Myth Busters shortly! [img]/images/graemlins/grin.gif[/img] The thread on their BB is over 45 pages long!!! [img]/images/graemlins/laugh.gif[/img]

[zeegler]

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

This thread should have been over a long time ago. So many people have tried to explain in so many logical ways why the plane will fly, and not one person has come up with a logical reason why the plane won't accelerate down the runway and take off. No one has explained how the plane is being held in place by the treadmill. Yet, they continue to hang on to the idea that it won't, logic and reason be damned. [img]/images/graemlins/laugh.gif[/img]

[Newc]

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

Why do the wheels on an airplane rotate?

[dg]

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

The wheels on a plane rotate in order to minimize friction. They do not produce any propulsion at all. They perform the same function as pontoons on a plane that takes off from the water. Wheels just happen to be the best way to reduce friction for a plane taking off from land. Since the plane is not relying on thrust produced by the wheels, the conveyor belt is irrelevent to its forward movement.

[Newc]

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

So do you agree that the wheels of the plane rotate because of the transference of energy originating as engine thrust?

[dg]

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

No thrust is transferred to the wheels. The wheels turn as a result of the forward movement of the plane. On a pontoon plane or a plane with skis that takes off from the snow, no propulsion is coming from those pontoons or skis. Wheels are the better alternative for pontoons or skis for a plane taking off from the ground.

[DumpyWumpy]

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

Ok I don't think anyone has mentioned this yet, and I am not sure which side I agree with but have at this...

Those of you suggesting that the plane will fly are suggesting that no matter what the conveyor is doing, the plane's speed relative to the ground is determined entirely by it's thrusters, as long as the plane's thrusters are turned on. 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, 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. 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. But turn on the planes engines and set them to 100MPH and what is the plane doing? Or, even set the plane to be moving at 50MPH...is the plane going to move slower than the conveyor belt that it's moving on in the SAME direction? I can't believe no one has brought this up in 18 fucking pages of crap [img]/images/graemlins/laugh.gif[/img]