There is a giant, 10 mile long stetch of runway with a 747 on the middle of it. The runway, however, is specially designed to move, much in the same way that a treadmill will move, in the opposite direction of the plane. Secondly, the treadmill is attached to a computer which will match the acceleration of the plane exactly and constantly, in the opposite direction.
What is the result of this experiment? Does the plane ever take off?
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Anonymous2006-11-01 23:20
if the plane isnt moving then its not going to get air resistance, so no lift.
>>5
The answer is blindingly obvious (>>2). I bet they had a twenty page thread about it though.
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Anonymous2006-11-02 11:40
>>6
LISTEN FUCKTARDS, THE PLANE TAKES OFF LIKE NORMAL
God I hate faggot failures who don't realize they are retarded
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Anonymous2006-11-02 12:21
>>7
You don't know anything about how a plane works. Go die.
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Anonymous2006-11-02 13:34
>>8
Go back to middle school, 4chan isn't good for kids like you
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Anonymous2006-11-02 13:59
>>9
So you think even a middle schooler would have a better understanding of physics than you?
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Anonymous2006-11-02 14:02
>>10
The plane takes off. It's obviously simple. The thrust from the engines works on the air around the plane, not on the runway.
Holy hell you have to be retarded not to realize that.
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Anonymous2006-11-02 14:46
>>11
Lift is generated by air resistance against the wings. If the plane isn't moving there's no (well, negligible) air resistance and thus negligible lift.
>>14 >>1
"The runway, however, is specially designed to move, much in the same way that a treadmill will move, in the opposite direction of the plane. Secondly, the treadmill is attached to a computer which will match the acceleration of the plane exactly and constantly, in the opposite direction."
yes......
So, what we have is a plane moving along thr runway, through that AIR at speed X, and a runway moving backwards against the AIR at a speed of X. Nowhere in the problem does it say the runway cancels out the movement of the speed, just that the runway will be moving in the opposite direction.
Since the plane recieves it's forward momentum by pushing against the AIR, not the runway, and since the wheels of a plane move freely, there is no way the runway can cancel the HUGE force of the plane engines simply by spinning the wheels faster
Go back to physics, plz
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Anonymous2006-11-02 17:21
>>16
The plane's position relative to the runway does not change, so assuming the runway is not itself moving forward at the rate one would expect the plane to move forward at, the relative wind against the plane is the exact same as if it were not moving at all.
>The plane's position relative to the runway does not change
False, the runway is moving in the opposite direction as the plane. Their relative positions are moving in the opposite directions very fast.
>so assuming the runway is not itself moving forward at the rate one would expect the plane to move forward at,
Are you assuming that the plane has its engines off? Because that's what it sounds like. If the runway wasn't moving at all, you admit that the plane would take off as normal, so I don't see the point of bringing up what would happen if the runway was moving in the SAME direction as the plane. That has nothing to do with the problem
>the relative wind against the plane is the exact same as if it were not moving at all.
Again, the plane is MOVING through the AIR at the same speed it normally would. The runway has NO effect (or very small effect) on the movement of the plane. This isn't hard to understand.
protip: if you run on a treadmill inside, you dont feel the wind in your face.
the science behind the troll argument is that its not like a car, the work produced by the engine isnt going into turning a driveshaft attached to the wheels, its going toward physically pushing the plane forward. however, as long as the plane is making contact with the treadmill, the backward movement of the runway will counteract the forward ROLLING of the wheels.
if the treadmill were moving the air with it, it would generate the necessary air resistance to generate the lift, however it is not. the plane will accelerate, and the indicated airspeed gauges on that plane will show the planes velocity increasing, however, all of this speed will work solely to maintain the planes physical position relative to the earth (and surrounding atmosphere), by counteracting the increasing speed of the treadmill runway.
if it would take off, that would mean youd be able to test the aerodynamics of a car by running it on a counteracting treadmill inside of a closed room, with no wind tunnel. i'm going to tell you right now, you could design a car shaped like an upright pancake and it would not have any negative impact on its performance under that test.
think about running on a treadmill to get a kite to start flying.
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Anonymous2006-11-02 18:03
Ok, since it seems people here are still in second grade, I'll use a childish analogy to explain my point.
You have a treadmill. Normal, simple treadmill.
Now, put a skateboard on the treadmill. Place your hand on top of it, holding it solidly.
Again the computer is attached so the speed of the treadmill is exactly the same as the speed of the skateboard, in the opposite direction.
Hold this all in your head... good...
Now, push the skateboard forward at 1 MPH. The computer instantly sends the treadmill backwards at 1 MPH.
But you can still easily pull the skateboard foward with your hand! The skateboard is moving forward at 1 MPH, the treadmill is moving backwards at 1 MPH, and the wheels of the skateboard are moving at 2 MPH (the difference).
Here's an even more obvious one. A treadmill is moving backwards at 20 MPH. You slowly set a skateboard on it, but hold it in place. The skateboard is moving at 0 MPH, the wheels at 20 MPH, and the treadmill at 20 MPH backwards.
You can still imagine moving the skateboard forward along that treadmill with your hand at 1 MPH. Now, the skateboard is moving at 1 MPH, the wheels at 21 MPH, the treadmill at 20 MPH.
The engines on the plane simply replace the force your hand is exerting on the skateboard. It will move forward and take off as normal.
Now GTFO
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Anonymous2006-11-02 18:55
>>20
thats because youre an external influence dumbass, youre not affected by the treadmill, the engines on the plane are ON THE FUCKING PLANE
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Anonymous2006-11-02 19:00
>>20
"You can still imagine moving the skateboard forward along that treadmill with your hand at 1 MPH. Now, the skateboard is moving at 1 MPH, the wheels at 21 MPH, the treadmill at 20 MPH."
Once again:
"Secondly, the treadmill is attached to a computer which will match the acceleration of the plane exactly and constantly, in the opposite direction."
Exactly and CONSTANTLY. If the plane starts to go faster, so does the treadmill - in the opposite direction. Jesus fucking Christ you're stupid.
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Anonymous2006-11-02 19:01
>>21
the engines are an external influence on the body of the plane just like your hand is an external influence on the body of the skateboard. You think the plane cares what the engines are connected to? Least time I checked, material objects weren't sentient.
ALL the body of the plane cares about is what forces are enacted on it. THAT'S IT. The engines are enacting a HUGE forward force onto it, IN THE EXACT SAME WAY your hand exertes a force on the skateboard. There is no difference at all. Ignoring the slight friction the wheels have on the runway-treadmill, they will spin freely as the treadmill moves. The momentum of the plane is far too much for the runway to overcome simply by spinning the wheels. Draw out a force diagram if you don't believe me, there is NO FORCE than can counter the force of the engines.
God these retards with no logical sense are pathetic
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Anonymous2006-11-02 19:13
the friction the wheels have on the parts of the plane theyre attached to is what matters.
Exactly! And as long as the wheels are well oiled and taken care of, the friction will be minimal
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Anonymous2006-11-02 20:19
lol wut, the plane takes off because of air speed not ground speed. Does the air move? well maybe only from your engines going full blast lol
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Anonymous2006-11-02 21:23
So many people are right for the wrong reasons.
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Anonymous2006-11-02 22:27
Although the runway treadmill is still moving at the same speed as the plane is still moving at whatever miles per hour. It can still take off. However, I suck at aerodynamics. So I don't have a clue bro. I'm thinking it would just crash.
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Anonymous2006-11-03 0:31
good god, planes take off because of air resistance not because the jets "push" the plane into the air. if there is no wind, the air is "still" in relation to the ground. under normal circumstances the jets will push the plane in relation to the ground, and thus air, in order to create lift on the wings as a result of air resistance. if the plane is not moving in relation to the ground, it therefor is not creating air resistance on the wings. no matter how much thrust you create in the jets the plane will not take off unless its moving in relation to the ground (assuming no wind). this is because the jets on the plane are for all of our purposes parellel to the earth.
I'm not saying that the plane will not be moving in relation to the air. Of course the jets aren't what push the plane into flight directly. No one is saying that.
The jets are, however, what push the plane forward relative to the air surrounding it. The jets on a treadmill will do exactly that, they will push the plane forward in relation to the air surrounding it. The treadmill will be moving backwards, but that will simply cause the wheels to speed up.
i thought over it and decided it could take off, and that the reason is because the opposite movement of the treadmill will not have any effect on the overall movement of the plane, but will in fact only cause the wheels to spin faster (twice as fast).
kind of like that trick where you pull the table cloth out from under a bunch of glasses, as long as the wheel-ground friction was greater, it would be able to move forward relative to the atmosphere, even though the conveyor was matching its speed. unlike a car, where the forward movement is generated BY the wheel-ground friction, a planes forward movement is generated by pushing against the air behind the jet.
ultimately, yes, the plane will take off, assuming the wheel-ground friction is greater than the wheel-against-the-plane friction.
also, the skateboard example is not very helpful, but has the right idea!
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Anonymous2006-11-03 1:25
continuing,
the reason the wheel against the ground friction has to be higher is so that when the treadmill runway pulls back, it turns the wheel rather than pulling the plane backward. the inertia of the plane do the work of keeping it nearly stationary and allowing the wheels to spin, and the jet thrust can be left to push the plane forward.
the point is, the wheels will be spinning as though the plane were moving twice as fast on a normal runway.
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Anonymous2006-11-03 1:25
>>30
Except for the part where he didn't match the acceleration, moron.
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Anonymous2006-11-03 1:28
>>32
continuing more,
this doesnt mean the runway could be any shorter than would be necessary under normal conditions, it would have to be at least as long, probably a longer, since the bearings arent perfectly frictionless.
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Anonymous2006-11-03 2:21
>>33
Are you blind, or a troll? It doesn't matter if he exactly matches the acceleration or not, it's obvious it has no effect on the speed of the skateboard (or very little). Since it obviously has no effect, your point is obviously wrong, and thus, logically, I am correct.
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Anonymous2006-11-03 3:02
The jet aircraft usually need at least 120 km/h of air travelling over their wings to take off.
If you're going to say that "The airplane is not moving relative to the air around it", then I suggest you look back at the posts which have already addessed that point and proven it wrong.