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Posted: 2/3/2007 8:43:58 PM EDT
[#1]
Okay, is this question assuming the airplane is in a controlled enviroment with no headwind?
Wheels on an airplane arent magic ball bearings, there will be resistance. I guess the question would be could you generate enough lift to take off assuming there was no head wind to assist the airplane. But what do I know, Im only a 15 hour Student pilot. 
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Posted: 2/3/2007 8:44:22 PM EDT
[#2]
Don't think friction has anything to do with it. It's about forward motion. |
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Posted: 2/3/2007 8:45:34 PM EDT
[#3]
This thread reminds me of the "can you make hamburgers with ground beef" thread.
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Posted: 2/3/2007 8:45:38 PM EDT
[#4]
Yes indeed. As the question is constructed, the conveyor will match speeds so as to keep the plane stationary. The plane's engine is applying thrust and the wheels are spinning, but there is no movement relative to a fixed point and no airspeed, since the air over the plane's wings is not affected. Imagine running on a treadmill. You're moving. The conveyor is moving. Is air rushing past you? No, it isn't, unless you're using a fan, which isn't stipulated in the question. The plane is affected the same way. |
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Posted: 2/3/2007 8:46:56 PM EDT
[#5]
How many peck of pickled peppers did peter piper finally end up with anyway?
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Posted: 2/3/2007 8:46:58 PM EDT
[#6]
Highlighted in red is what makes the question so stupid. The assumption is incorrect. As I said before, I might as structure my answer to it with an assumption that the plane is question has an antigravity propulsion system.
Poor example. I don't take off in my plane by putting the transmission in "D' and hitting the gas pedal. |
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Posted: 2/3/2007 8:47:13 PM EDT
[#7]
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Posted: 2/3/2007 8:48:07 PM EDT
[#8]
See, the way I was looking at it was that the conveyor WAS implying friction - ie the friction between the wheel and the axle pushing the aircraft backwards while the engines are pushing the aircraft forward, thus result into zero forward movement through the air, resulting in no lift. |
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Posted: 2/3/2007 8:48:11 PM EDT
[#9]
Im confused. Is the plane moving in relation to the air around it or is it stationary?
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Posted: 2/3/2007 8:48:21 PM EDT
[#10]
I'm assuming the plane is powered by some thrust generating device like a jet engine or a prop. I think the real question is, is the conveyor belt bolted to the wheels and the ground? |
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Posted: 2/3/2007 8:48:52 PM EDT
[#11]
We are all missing the more important question, could you land it on the conveyer belt?
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Posted: 2/3/2007 8:49:23 PM EDT
[#12]
How does that come into play here? |
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Posted: 2/3/2007 8:49:44 PM EDT
[#13]
The plane is stationary relative to the air. |
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Posted: 2/3/2007 8:50:42 PM EDT
[#14]
Why? How is a conveyor belt holding the plane still? |
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Posted: 2/3/2007 8:51:49 PM EDT
[#15]
Yes, the airplane will take off. Why? Because F=ma. The thrust from the engine will propel it forward, regardless of what the conveyer belt is doing. Most folks think that a conveyer belt can thwart forward movement because they are used to pushing against the ground to move and a conveyer belt moving the opposite direction can negate their efforts to move forward. However, all airplane propulsion (whether prop or jet) pushes against the air, generating thrust, which causes accelleration, regardless of what the surface below the wheels is doing (assuming the brakes are off). edited to add: another way to think of this problem is to realize that the brakes are off - therefore, the wheels spin freely and the conveyer belt really doesn't cause any force on the plane at all (neglecting friction, which is negligible compared to thrust). |
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Posted: 2/3/2007 8:52:21 PM EDT
[#16]
Oh, God. Oh, dear God. Words fail me. Oh my God, some of you are what happens when the kids who don't pay attention in my physics classes grow up. I just...wow. Damn. One or two leading questions, for those of you who think (quite wrongly) that the plane couldn't take off: does a plane's engines push against the GROUND? If not, what DO the plane's engines push against to get their thrust? |
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Posted: 2/3/2007 8:52:35 PM EDT
[#17]
Because it's rolling backwards at the same velocity as the plane is rolling forwards, resulting in a net velocity of zero. Just like when you run on a treadmill. |
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Posted: 2/3/2007 8:53:34 PM EDT
[#18]
Read the link...................... I don't spoon feed. |
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Posted: 2/3/2007 8:53:48 PM EDT
[#19]
Well, I took 6 years worth of physics classes. The riddle is stupid. The answers are stupid. What does a conveyor belt have to do with anything since the forward thrust on the airplane is not acting at the wheels? Why would you suppose there is a giant headwind? Where does it say that in the question? How about if the earth exploded and the plane was ejected into space? How about if a tornado lifted the plane? Dumb. |
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Posted: 2/3/2007 8:54:16 PM EDT
[#20]
Maybe the wheels are moving so fast on the conveyor belt that the friction in the bearings is enough to balance the plane's thrust. |
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Posted: 2/3/2007 8:54:28 PM EDT
[#21]
Wrong, I do burnouts at the end of the runway all the time. I dump the clutch and listen to those tires scream.
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Posted: 2/3/2007 8:54:49 PM EDT
[#22]
Then why doesn't an airplane with the brakes locked take off? |
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Posted: 2/3/2007 8:55:30 PM EDT
[#23]
On a treadmill, you run with your legs, pushing against the ground for thrust. Airplanes' engines push against the air... the ground has little to do with it. |
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Posted: 2/3/2007 8:55:40 PM EDT
[#24]
Think about why this question was asked in the first place.
Can the plane over come the handicap of a conveyor belt under it and take off? More than likely, yes, but that is not why this stupid question is bouncing around the internet. It is because some "genius" got the notion in his head that you could eliminate the long runway and just have a belt spin the wheels up to take off speed, in which case, no, it won't work. Ground speed has nothing to do with take off. In the instance given in the op's post, yes, it would take off. In the retarded spirit of the concept to begin with, no, you cannot shorten the take off distance by placing a conveyor belt under the plane. |
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Posted: 2/3/2007 8:55:55 PM EDT
[#25]
I did. Do you wipe? |
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Posted: 2/3/2007 8:55:57 PM EDT
[#26]
That's what I've been going for - but it's not defined in the hypothetical. |
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Posted: 2/3/2007 8:56:01 PM EDT
[#27]
Jesus... Christ. This is ABSOLUTELY NOTHING LIKE RUNNING ON A TREADMILL! When running on a treadmill, your legs--which are also the force in contact with the treadmill--are providing forward motion. The plane's wheels have NOTHING to do with imparting forward motion. The question is flawed! |
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Posted: 2/3/2007 8:56:52 PM EDT
[#28]
You are woefully missing the point - as has been stated multiple times, the assumption that a spinning conveyor COULD stop forward motion in the first place is wrong. |
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Posted: 2/3/2007 8:57:20 PM EDT
[#29]
They interact with the air, not the ground. They use it to develop velocity. It is the velocity of the air flowing over the wing that creates lift and allows them to take off (again, assuming the plane is not a rocket, nor a helicopter, nor a VTOL). No matter how fast you run on that treadmill, you will not develop any velocity relative to the air nor the ground. You will only develop relative velocity to the treadmill's belt. The plane will only develop relative velocity to the conveyor. It will have no air flowing over the wings. It will not take off. And I earned an A in both physics 207 and 208, thank you very much. |
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Posted: 2/3/2007 8:57:49 PM EDT
[#30]
Then why do they put brakes on landing gear? |
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Posted: 2/3/2007 8:58:33 PM EDT
[#31]
Because it is held in place by friction against the ground. How will a treadmill provide that friction? Spinning fast enough to overheat the plane's wheel bearings? ETA: I think what I'm trying to say is that the question is retarded to begin with. |
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Posted: 2/3/2007 8:59:13 PM EDT
[#32]
Because you have increased the effective coefficient of friction between the plane's body and the ground. Without brakes applied, you have bearings designed to *minimize* the friction between the two; the brakes are designed to *maximize* the friction. |
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Posted: 2/3/2007 9:00:04 PM EDT
[#33]
Give this man a prize, he understands it. |
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Posted: 2/3/2007 9:01:30 PM EDT
[#34]
Yeah, the bearing minimize friction but they don't remove it. |
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Posted: 2/3/2007 9:01:46 PM EDT
[#35]
fuck it. IBTL Some people are just too fucking stupid |
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Posted: 2/3/2007 9:02:03 PM EDT
[#36]
A treadmill isn't going to matter squat, air speed comes from the propeller pulling the plane forward through the air, which for the purpose of the conveyor argument is a stable medium, and as it moves forward air speed over the wings provides lift.
Conveyor belt has no direct effect on air flow over the wings. Sure, as the plate reaches take off speed the wheels will be going much faster than if taking off on a stationary runway, big whoop. Change it to a head wind that matches the take off airspeed of the aircraft and maybe you'll have something but air speed over the wings is still going to generate lift at which point it is still technically flying. |
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Posted: 2/3/2007 9:02:13 PM EDT
[#37]
Have fun....My plane won't take off. Your plane can do whatever it wants.
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Posted: 2/3/2007 9:02:47 PM EDT
[#38]
You're making the logical leap from an airplane engine developing its thrust by moving air, to a person running on a treadmill whose only source of thrust is a frictional interaction with the treadmill. You're not analyzing the problem accurately. |
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Posted: 2/3/2007 9:03:03 PM EDT
[#39]
No, he's ignored the stated problem. The problem clearly states: "The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction." It doesn't state that the conveyer belt will move at whatever speed is necessary to stop forward movement. Edited to add: the question is meant to trip up dolts who think that an airplane moving 100 mph can somehow be held motionless by a treadmill underneath moving 100 mph in the opposite direction. BTW, the wheel bearings can easily handle speeds twice the takeoff speed of an aircraft, so don't even think that friction is going to stop it. |
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Posted: 2/3/2007 9:03:18 PM EDT
[#40]
Notice the edit-- I left out "imparting" An aircraft's landing gear does not impart forward motion. It is free-spinning. It is not powered. It does not produce torque. You can't drop the fucking clutch. The question is flawed. If I eliminate all logic, and say that the conveyor holds the aircraft stationary relative to a fixed object, then of course it would not take off. We are challenging that premise of the question, it is not possible. The wheels might as well be skids. |
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Posted: 2/3/2007 9:03:26 PM EDT
[#41]
So airplanes with shitty wheel bearings turn into fireballs at the end of runways? I use really good grease in MY wheel bearings, along with larger wheels (uh, oh, another riddle awaits) just for these occasions. 
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Posted: 2/3/2007 9:05:07 PM EDT
[#42]
So are there wheels on the bottom of the treadmill? I guess I am assuming that the thing is bolted down. ETA: I guess when the wheel friction gets high enough, the wheel can just slide forward off the conveyor belt. |
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Posted: 2/3/2007 9:05:46 PM EDT
[#43]
"Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"
On second thought I'm sure the plane will take off but the wheels will rotate faster then normal. As some have said forward thrust is independent of the wheels. Neglecting the friction of the wheel bearings. |
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Posted: 2/3/2007 9:05:54 PM EDT
[#44]
I don't know how much friction the bearings-wheel-tire-runway system develops, but I suspect that it would take a treadmill moving at many hundreds, if not thousands, of miles per hour to produce enough force to impede the acceleration of the aircraft...at least until the tires blew and the plane started to skid on its struts. I'm not posting further in this thread, as I suspect it is someone's troll project. At least I hope it is. |
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Posted: 2/3/2007 9:08:46 PM EDT
[#45]
So if an aircraft is up on jacks and you spin the wheels, they'll spin eternally? |
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Posted: 2/3/2007 9:09:01 PM EDT
[#46]
The engines don't push against anything. A rocket engine works the same in a vacuum as it does in the atmosphere. Pressure inside the engine pushes the rocket forward. Same thing with a jet engine. I could show you this in 2 seconds with a chalkboard. It's hard to put into words. Think about this: a ported gun shoves the muzzle down because for an instant there is a LOT of pressure on the bottom of the barrel but NO pressure on the top of the barrel where the holes are. Similarly, there is a LOT of pressure on the TOP of a rocket engine combustion chamber but NO pressure at the nozzle. Just a hole on that end. The high pressure expanding gas inside the engine pushes the rocket forward. Think about it. Look it up if you don't believe me. |
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Posted: 2/3/2007 9:09:22 PM EDT
[#47]
That's the exact absurd situation I was shooting for, trying to explain why this is a stupid question to begin with. |
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Posted: 2/3/2007 9:11:01 PM EDT
[#48]
No, I'm using that as an example, since people don't seem to be able to comprehend that an object can be "still" even while moving on a conveyor. The source of the thrust does not matter; all that matters is the presence or absence of air moving over the plane's wings. If the plane is not moving relative to anything except the conveyor, and the air is not moving relative to the plane, the plane will not take off.
If the belt is perfectly matching the speed of the wheels, then the plane is not moving forward. |
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Posted: 2/3/2007 9:11:06 PM EDT
[#49]
the poster on the other board may very well have meant to troll with it.
i promise i did not. i don't know anything about physics. |
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Posted: 2/3/2007 9:11:06 PM EDT
[#50]
There's a 466 page thread here if you want to argue: forum.physorg.com/index.php?showtopic=2417.
The plane will take off with the wheels spinning twice as fast as normal is the correct answer. ETA: Oops, should have read more carefully. I assumed you used the classic problem, not the reworded one that specifically states wheels. The practical/real world answer to your version is the that plane will overpower the conveyor and the plane will take off (assuming nothing breaks.) |
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