Can A Plane Take Off On A Treadmill?
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From: Calgary
Originally Posted by i_heart_my_DB8,Jan 28 2008, 10:13 PM
The treadmill doesn't need to create its own gravity, as the earth is providing more than enough to keep the plane's wheels securely planted on the treadmill, which is more than enough in this case to make a difference. I imagine in space, a plane can "sit" on a treadmill all day long, spinning its own wheels and not going anywhere.
I know what you're saying, trust me, I'm not some bumblef**k desktop engineer who can't figure out that the plane isn't being driven by the wheels.
However, I suppose there's a lot to be said in exactly *how* this plane and treadmill operation comes into play.
If the plane is ON the treadmill, and the treadmill starts moving backwards at 1000 mph, the plane is going to start moving backwards at 1000 mph. You're telling me that the energy to overcome that 1000 mph handicap is going to be the same as it would be to take off from 0?
I know what you're saying, trust me, I'm not some bumblef**k desktop engineer who can't figure out that the plane isn't being driven by the wheels.
However, I suppose there's a lot to be said in exactly *how* this plane and treadmill operation comes into play.
If the plane is ON the treadmill, and the treadmill starts moving backwards at 1000 mph, the plane is going to start moving backwards at 1000 mph. You're telling me that the energy to overcome that 1000 mph handicap is going to be the same as it would be to take off from 0?
But you don't have to exactly equally counter the speed of the treadmill to stay stationary. You could hold that bag on the moving walkway with just a little bit of hand strength, probably with just a finger or two. You're hardly exerting the same force in one direction that the treadmill is exerting in the other.
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From: San Diego, Wess-Side!!
Originally Posted by i_heart_my_DB8,Jan 28 2008, 09:00 PM
Sorry Tim, I don't believe this to be true.
Think of it like this: The earth is moving, yes? Think of the earth as a giant treadmill.
Now... do planes parked on an airstrip roll along freely above the earth (giant treadmill)? No. They move WITH THE EARTH (giant treadmill).
It's only enough thrust to create enough forward movement IN ADDITION to the movement of the treadmill that the plane will take off.
Think of it like this: The earth is moving, yes? Think of the earth as a giant treadmill.
Now... do planes parked on an airstrip roll along freely above the earth (giant treadmill)? No. They move WITH THE EARTH (giant treadmill).
It's only enough thrust to create enough forward movement IN ADDITION to the movement of the treadmill that the plane will take off.
Let's not start with relative motion.
If you put a frictionless free spinning wheel on a treadmill and then glue on some buildings to the treadmill and then turn it on. The buildings will move and the free spinning wheels will not.
Friction is what will cause the plane to move backwards with your scenario but my scenario is solely for the purpose to show that the plane will infact move FORWARD with thrust and it WILL take off.
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From: Scatterbrainia
Originally Posted by SIIK2NR,Jan 28 2008, 11:43 PM
Yes the earth is moving but so it the plane and moving at the same speed. There for relative to everything else that is viewing it.... it is not moving. Therefore the earth is not a treadmill.
Let's not start with relative motion.
If you put a frictionless free spinning wheel on a treadmill and then glue on some buildings to the treadmill and then turn it on. The buildings will move and the free spinning wheels will not.
Friction is what will cause the plane to move backwards with your scenario but my scenario is solely for the purpose to show that the plane will infact move FORWARD with thrust and it WILL take off.
Let's not start with relative motion.
If you put a frictionless free spinning wheel on a treadmill and then glue on some buildings to the treadmill and then turn it on. The buildings will move and the free spinning wheels will not.
Friction is what will cause the plane to move backwards with your scenario but my scenario is solely for the purpose to show that the plane will infact move FORWARD with thrust and it WILL take off.
To your response Tim, (and the one above it by MikeyCB), I don't know whether or not the plane will take off. All I know is that there are too many variables to simply say: "Dude, it WILL take off, because it's not driven by the wheels."
MikeyCB has already admitted that it will take *some* effort to hold the plane in place on the treadmill. So we can already deduce that the treadmill has *some* effect on the plane.
Here's what we do know: There IS gravity. There IS friction.
Put a bowling ball on the treadmill and turn it on. Guess what? The bowling ball rolls off the back of the treadmill.
Remember the science experiment where you pull the tablecloth out from under the dishes? And how if you pull it really quick, everything stays put? But if you pull it slowly, the dishes fall off the table? Well, I suppose if you could place the plane on a treadmill that was stationary, and then kick start the treadmill with enough force to get it going *immediately*, I suppose the plane might stay still. However, I do imagine it would be some engineering feat to first construct a treadmill large enough for a plane, let alone get it to start going immediately
.
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From: Brazoria
The trick to solving these problems is take them in steps. Step number one is turning on the belt with the airplane on it. There may be a bit of initial slippage due do the wheel's spinning before they begin to grab fully (relative to the friction between belt and wheel) and the plane moves backwards. Step two is to bring the plane to a speed consistent with that of the belt. That is to say; make it stop. How much force is require to do this? Very little, only enough to overcome the friction between belt and wheel. Picture it this way; You are on a treadmill wearing roller skates. To stop you from moving backwards all I have to do is put an tiny amount of pressure on your back (a pinky finger's worth would suffice), I don't need to apply 150 founds of pressure because you weigh 150lbs. I need only defeat friction. At this point any additional energy applied would propel the plane forward, and the plane's engine would have plenty of power to spare. It would need a longer runway, but it would not be an exceptional amount.
but here's some interesting stuff regarding the flaws of the question:
Given this, the really interesting part of this problem lies in how the conveyor belt's control is programmed. "The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction." If this is taken literally one could argue that, since the wheels start at zero RPM and are not being forced to turn, the conveyor should hold the wheels at zero regardless of the plane's motion (-0 = 0). Thus, the conveyor would follow the plane's motion, and the plane would take off with the wheels at rest.
Or, we could interpret it as the author would mislead us into thinking, that the conveyor should move opposite the plane's attempted motion at a rate sufficient to keep it in place. Since the conveyor cannot prevent that motion, in theory its backward speed will quickly go to infinity. At which point the plane may fly through a wormhole to its destination, saving much time and fuel. Or a black hole will form that ingests plane, conveyor, and eventually Earth. I look forward to the experiment. I think.
he difference, however, is that as the plane started to move, the wheels of the plane would turn, and the fictional treadmill would increase in speed to match ... which would cause the wheels to turn faster, thus causing the treadmill to move faster, etc ... a mutually reinforcing system, until the wheels and the treadmill both turned to molten lava (and how fast that happens depends on how closely the treadmill could match wheel speed). Meanwhile, the body of the plane would be busy taking off as usual, unaware of the drama happening below (except, perhaps, for the smell of melting rubber).
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From: Calgary
Originally Posted by i_heart_my_DB8,Jan 29 2008, 12:00 AM
Oh come on... no friction? Now you're just talking crazy!!!
To your response Tim, (and the one above it by MikeyCB), I don't know whether or not the plane will take off. All I know is that there are too many variables to simply say: "Dude, it WILL take off, because it's not driven by the wheels."
MikeyCB has already admitted that it will take *some* effort to hold the plane in place on the treadmill. So we can already deduce that the treadmill has *some* effect on the plane.
Here's what we do know: There IS gravity. There IS friction.
Put a bowling ball on the treadmill and turn it on. Guess what? The bowling ball rolls off the back of the treadmill.
Remember the science experiment where you pull the tablecloth out from under the dishes? And how if you pull it really quick, everything stays put? But if you pull it slowly, the dishes fall off the table? Well, I suppose if you could place the plane on a treadmill that was stationary, and then kick start the treadmill with enough force to get it going *immediately*, I suppose the plane might stay still. However, I do imagine it would be some engineering feat to first construct a treadmill large enough for a plane, let alone get it to start going immediately.
To your response Tim, (and the one above it by MikeyCB), I don't know whether or not the plane will take off. All I know is that there are too many variables to simply say: "Dude, it WILL take off, because it's not driven by the wheels."
MikeyCB has already admitted that it will take *some* effort to hold the plane in place on the treadmill. So we can already deduce that the treadmill has *some* effect on the plane.
Here's what we do know: There IS gravity. There IS friction.
Put a bowling ball on the treadmill and turn it on. Guess what? The bowling ball rolls off the back of the treadmill.
Remember the science experiment where you pull the tablecloth out from under the dishes? And how if you pull it really quick, everything stays put? But if you pull it slowly, the dishes fall off the table? Well, I suppose if you could place the plane on a treadmill that was stationary, and then kick start the treadmill with enough force to get it going *immediately*, I suppose the plane might stay still. However, I do imagine it would be some engineering feat to first construct a treadmill large enough for a plane, let alone get it to start going immediately
.I was on your side of considering why it wouldn't take off until I really sat down and logically thought about this. Obviously no hard numbers involved in the thought process, but that's not my kind of logic anyway
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From: Hollywood
Originally Posted by i_heart_my_DB8,Jan 28 2008, 09:13 PM
If the plane is ON the treadmill, and the treadmill starts moving backwards at 1000 mph, the plane is going to start moving backwards at 1000 mph. You're telling me that the energy to overcome that 1000 mph handicap is going to be the same as it would be to take off from 0?
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From: Scatterbrainia
Originally Posted by MikeyCB,Jan 29 2008, 01:32 AM
I grew up with a kid like you...you like debates, my friend, don't you
I was on your side of considering why it wouldn't take off until I really sat down and logically thought about this. Obviously no hard numbers involved in the thought process, but that's not my kind of logic anyway
I was on your side of considering why it wouldn't take off until I really sat down and logically thought about this. Obviously no hard numbers involved in the thought process, but that's not my kind of logic anyway