Poulsonator
Golden Member
- Aug 19, 2002
- 1,597
- 0
- 76
For those "non-taker-offers", what's your take on this? This is the best example used in the thread yet on why the plane would take off.
For those "non-taker-offers", what's your take on this? This is the best example used in the thread yet on why the plane would take off.
He is wrong. The truck would not move it would sit there spinning its whells in the dirt. They only way it could move is to violate the speed of the treadmill matching the speed of the wheels.
Actually, the 2nd part of his statement is correct. The skateboard will move forward, but only by its wheels moving faster than the treadmill.
zinfamous
No Lifer
- Jul 12, 2006
- 111,857
- 31,346
- 146
I'm sure that if mythbusters does tackle this problem, and reaches the type of conclusion that they tend to reach, another thread will begin on here debating the results of their conclusion and the very same string of arguments between idiots, imbeciles, and people with way too much time on their hands, will continue unabated.
exdeath
Lifer
- Jan 29, 2004
- 13,679
- 10
- 81
Originally posted by: zinfamous
I'm sure that if mythbusters does tackle this problem, and reaches the type of conclusion that they tend to reach, another thread will begin on here debating the results of their conclusion and the very same string of arguments between idiots, imbeciles, and people with way too much time on their hands, will continue unabated.
All they have to do is borrow a factory or plant of some kind that has a large single run of conveyer and drop a running model airplane on it.
Turn on the belt and hit full throttle on the plane remote at the same time. Since it would be too complicated to precisely match the conveyer speed to the forward speed of the plane at the exact same time, they could predetermine a throttle position of the model airplane on still ground that results in a forward speed that matches the conveyer system selected; a speed that is sufficient for take off. Then with the throttle held to that position, drop the plane on an already moving conveyer belt.
I predict the plane would travel backwards along the conveyer for a brief instant, come to a rest, then proceed forward and take off, as the engine trust compensates for the initial momentum of the plane traveling on the conveyer belt.
If you wanted to exaggerate the fact that the plane can still take off regardless of the conveyer, you could even start the conveyer at full speed and start the plane at a deficit at idle. You would need enough space behind the plane for rearward travel until the thrust momentum builds up and compensates for the initial rearward inertia, and enough space in front to attain take off velocity shortly after.
It can be assumed then if the plane can recover from a Vconveyer > Vplane initial condition, than it would have even less of a problem with a Vconveyer = Vplane initial condition. The only difference is lack of the initial rearward movement and the time it takes to take off.
Originally posted by: exdeath
Originally posted by: zinfamous
I'm sure that if mythbusters does tackle this problem, and reaches the type of conclusion that they tend to reach, another thread will begin on here debating the results of their conclusion and the very same string of arguments between idiots, imbeciles, and people with way too much time on their hands, will continue unabated.
All they have to do is borrow a factory or plant of some kind that has a large single run of conveyer and drop a running model airplane on it.
Turn on the belt and hit full throttle on the plane remote at the same time. Since it would be too complicated to precisely match the conveyer speed to the forward speed of the plane at the exact same time, they could predetermine a throttle position of the model airplane on still ground that results in a forward speed that matches the conveyer system selected; a speed that is sufficient for take off. Then with the throttle held to that position, drop the plane on an already moving conveyer belt.
I predict the plane would travel backwards along the conveyer for a brief instant, come to a rest, then proceed forward and take off, as the engine trust compensates for the initial momentum of the plane traveling on the conveyer belt.
If you wanted to exaggerate the fact that the plane can still take off regardless of the conveyer, you could even start the conveyer at full speed and start the plane at a deficit at idle. You would need enough space behind the plane for rearward travel until the thrust momentum builds up and compensates for the initial rearward inertia, and enough space in front to attain take off velocity shortly after.
It can be assumed then if the plane can recover from a Vconveyer > Vplane initial condition, than it would have even less of a problem with a Vconveyer = Vplane initial condition. The only difference is lack of the initial rearward movement and the time it takes to take off.
You can't do any experiment and have valid results. The question is therorical.
One could easily create this experiment on small scale. The question is not "therorical", whatever that means.
It absolutely is theoretical. As has already been explained. Such a device does not exist in the real world as it's possible of infinite acceleration as outlined by the original question.
Even if you convince yourself that you can't test the plane, you could certainly test this:
I mean, come on. Do you really believe this? It's the same as the whole treadmill/matchbox car argument from before. If you had your finger on a matchbox car that was on a treadmill, do you really think that the treadmill could stop you from pushing the car forward?
Well, whatever. You couldn't possibly believe that, so you are just a troll at this point.
A real treadmill would be unable to stop the truck but that doesn't matter.
We are not talking about a real treadmil.
The key to this problem is that the force of friction has an upper bound. Ff = u N
u : coefficient of friction
N : normal force
Ff : MAXIMUM force of friction
What is the normal force in this scenario? It is perpendicular to the direction of motion: the weight of the aircraft. Note that the speed of the treadmill does not matter!
The treadmill can exert a maximum of Ff on the wheels. It can exert less, but never more than Ff. Even if the treadmill is moving at infinite speed it is only exerting Ff on the wheels.
All that is necessary is the thrust of the plane's engines exceed Ff, which is a finite quantity.
u : coefficient of friction
N : normal force
Ff : MAXIMUM force of friction
What is the normal force in this scenario? It is perpendicular to the direction of motion: the weight of the aircraft. Note that the speed of the treadmill does not matter!
The treadmill can exert a maximum of Ff on the wheels. It can exert less, but never more than Ff. Even if the treadmill is moving at infinite speed it is only exerting Ff on the wheels.
All that is necessary is the thrust of the plane's engines exceed Ff, which is a finite quantity.
Cerpin Taxt
Lifer
- Feb 23, 2005
- 11,940
- 542
- 126
It has never been about the speed of the wheels. It has always been about the speed of the plane. You've been told this several times already, yet you persist under your obviously mistaken interpretation.
At this point, there is nothing left to conclude but that you are doing so deliberately, meaning you are trolling. What on earth motivates you to do such a thing? Mommy and Daddy didn't give you enough attention?
you seem geniunely not a troll. so i will try and explain it to you. there are two possible interpretations and that is the problem here.
1. the treadmill matches the speed of the airplane relative to the ground/atmosphere.
2. the treadmill matches the speed of the airplane relative to its own(the treadmill's) surface.
now case 1 is the most obvious and logical interpretation. since by your own admission case 2 is impossible. in case 1 you do not need infinite acceleration, the treadmill only needs to match the acceleration of the airplane, which is not infinite. In case 2, acceleration doesnt matter at all, since the treadmill can never(its impossible) match the airplanes speed relative to itself, the only time it does match is at zero.
Case 1 is not the most obvious or logical interpretation. When people think about treadmills they consider the speed of the object on the treadmill with reference to the treadmill surface. Go down to a gym and ask 10 people how fast are they running and 99% of them will give a speed that references the treadmill surface and not ground. So in fact case 2 is the most obvious interpolation of the question.
Oh in case you can't figure it out wheel speed is the same as plane speed with reference to the treadmill.
If the treadmill is free running so that it matches the velocity of the plane relative to the ground, then the plane will take off for all the reasons already mentioned with the wheels spinning at twice the usual angular velocity.
If the treadmill is programmed to match the rotational speed of the wheels at the circumference, then the wheels are going to speed up exponentially, the bearings will eventually seize (or the tyres will explode) and the landing gear will get ripped off causing massive structural damage to the plane.
In the real world you would expect some form of explosion.
In a test environment with a model plane you'll get a confused gym patron with a toy plane stuck up his ass.
John
If the treadmill is programmed to match the rotational speed of the wheels at the circumference, then the wheels are going to speed up exponentially, the bearings will eventually seize (or the tyres will explode) and the landing gear will get ripped off causing massive structural damage to the plane.
In the real world you would expect some form of explosion.
In a test environment with a model plane you'll get a confused gym patron with a toy plane stuck up his ass.
John
So you guys (Spidey and Smackdown) are proposing that the argument is theorical because the only way in which the treadmill could compensate for thrust is if it was a 'special theoritcal'? I think that the only theoretical part of the question is the friction and the speed matching capability of the treadmill.
Rogo
Rogo
Here is what will happen:
The plane needs air moving over it's wings. Without that wind the plane can NOT use it's flaps to angle them up to cause pressure to get the plane into the air.
YES thrust can move it forward even when not on a treadmill but it HAS to have that wind to get it in the air. If it does not have this the plane will just continue to move forward and not ever get lift and fly. (We are of course assuming that the engines are pointed streight ahead like a normal plane)
It will put it's flaps up and NOTHING will happen. It will just sit there. Like a plane with no wings. So if the flaps are useless HOW can the plane take off? It can't. A plane with no flaps or useless flaps cant take off. Thats how a plane works.
But it can cause forward FORCE. So if the treadmill/conveyor belt matches it's force it will forever stay on the ground. Yes there is thrust to give it forward push but it will be matched by the treadmill so it will stay in one place ONLY causeing foward force but not taking off. It can not go any faster than the treadmill because if whatever force the plane uses to be able to make it push ahead even one inch on the treadmill the treadmill will compensate and speed up to a point that is equal to what that plane needed to move ahead. Using only what is on it's side....gravity and friction (the treadmills side). So it will never move that inch or any at all foward.
Now...however the plane is still causeing air to be moved. through it's engines. At some point and some power of thrust the plane is going to be sucking so much air through that area that eventually it's going to cause the entire atmosphere to start moving and passing over it's wings also. At this point it will start to build up wind speed over it's wings. This will take an amazing amount of thrust and way above it's normal speed. At some point it will be fast enough to make the flaps usefull. At that second those flaps can give it some lift the plane will pull up and shoot foward with insane speed and rocket off that treadmill now that there is no more force pushing against it's wheels and causeing friction on the wheels, bearings etc (since it is no longer in contact with the treadmill at all). And it will be flying. Now it will be airborn and using air pressure and wind speed to keep it up.
Now if you have a prop plane this will happen much faster since the prop is in front of the flaps and pushing wind over the wings. Making the flaps usefull much sooner. But once it gets off the ground it will have to have enough force to propell it forward fast enough to catch enough air pressure to keep it up after it leaves the threadmill.
*some side notes*: A plane in space will NOT be able to take off (assuming it has air suppied to the jet fuel to ignite it). It would ONLY be able to move FORWARD. Flaps would be useless with no air in space unless postioned behind the engine thrust or the engine actually moved itself. This is why the plane would just sit there on a treadmill and not get lift at first. Thrust can push it foward it can't steer it.
*2nd note*: Put the plane on the treadmill. Start the treadmill.... what happens? It goes backward. Apply thust to keep it in one place. Then make the treadmill move faster.... the plane will now have to apply even more thrust to keep it from falling behind. So it does take power and thrust to compensate for the friction and gravity and whatnot. And that increases as the threadmill moves faster. I know it sounded bizzare at first but that guy that said the truck would just spin tires if pulling someone on a treadmill is correct. If that treadmill is moving 1000 MPH (random speed I chose) its going to be causeing an insane amount of pull back on that truck. The point in mentioning this is basicly that the faster the treadmill goes the more force back it will cause and if it can go to any speed it can match any force moving forward.
So in a way both sides are correct up to a point
The plane needs air moving over it's wings. Without that wind the plane can NOT use it's flaps to angle them up to cause pressure to get the plane into the air.
YES thrust can move it forward even when not on a treadmill but it HAS to have that wind to get it in the air. If it does not have this the plane will just continue to move forward and not ever get lift and fly. (We are of course assuming that the engines are pointed streight ahead like a normal plane)
It will put it's flaps up and NOTHING will happen. It will just sit there. Like a plane with no wings. So if the flaps are useless HOW can the plane take off? It can't. A plane with no flaps or useless flaps cant take off. Thats how a plane works.
But it can cause forward FORCE. So if the treadmill/conveyor belt matches it's force it will forever stay on the ground. Yes there is thrust to give it forward push but it will be matched by the treadmill so it will stay in one place ONLY causeing foward force but not taking off. It can not go any faster than the treadmill because if whatever force the plane uses to be able to make it push ahead even one inch on the treadmill the treadmill will compensate and speed up to a point that is equal to what that plane needed to move ahead. Using only what is on it's side....gravity and friction (the treadmills side). So it will never move that inch or any at all foward.
Now...however the plane is still causeing air to be moved. through it's engines. At some point and some power of thrust the plane is going to be sucking so much air through that area that eventually it's going to cause the entire atmosphere to start moving and passing over it's wings also. At this point it will start to build up wind speed over it's wings. This will take an amazing amount of thrust and way above it's normal speed. At some point it will be fast enough to make the flaps usefull. At that second those flaps can give it some lift the plane will pull up and shoot foward with insane speed and rocket off that treadmill now that there is no more force pushing against it's wheels and causeing friction on the wheels, bearings etc (since it is no longer in contact with the treadmill at all). And it will be flying. Now it will be airborn and using air pressure and wind speed to keep it up.
Now if you have a prop plane this will happen much faster since the prop is in front of the flaps and pushing wind over the wings. Making the flaps usefull much sooner. But once it gets off the ground it will have to have enough force to propell it forward fast enough to catch enough air pressure to keep it up after it leaves the threadmill.
*some side notes*: A plane in space will NOT be able to take off (assuming it has air suppied to the jet fuel to ignite it). It would ONLY be able to move FORWARD. Flaps would be useless with no air in space unless postioned behind the engine thrust or the engine actually moved itself. This is why the plane would just sit there on a treadmill and not get lift at first. Thrust can push it foward it can't steer it.
*2nd note*: Put the plane on the treadmill. Start the treadmill.... what happens? It goes backward. Apply thust to keep it in one place. Then make the treadmill move faster.... the plane will now have to apply even more thrust to keep it from falling behind. So it does take power and thrust to compensate for the friction and gravity and whatnot. And that increases as the threadmill moves faster. I know it sounded bizzare at first but that guy that said the truck would just spin tires if pulling someone on a treadmill is correct. If that treadmill is moving 1000 MPH (random speed I chose) its going to be causeing an insane amount of pull back on that truck. The point in mentioning this is basicly that the faster the treadmill goes the more force back it will cause and if it can go to any speed it can match any force moving forward.
So in a way both sides are correct up to a point
Number1
Diamond Member
- Feb 24, 2006
- 7,881
- 549
- 126
Originally posted by: tk109
Here is what will happen:
The plane needs air moving over it's wings. Without that wind the plane can NOT use it's flaps to angle them up to cause pressure to get the plane into the air.
YES thrust can move it forward even when not on a treadmill but it HAS to have that wind to get it in the air. If it does not have this the plane will just continue to move forward and not ever get lift and fly. (We are of course assuming that the engines are pointed streight ahead like a normal plane)
It will put it's flaps up and NOTHING will happen. It will just sit there. Like a plane with no wings. So if the flaps are useless HOW can the plane take off? It can't. A plane with no flaps or useless flaps cant take off. Thats how a plane works.
But it can cause forward FORCE. So if the treadmill/conveyor belt matches it's force it will forever stay on the ground. Yes there is thrust to give it forward push but it will be matched by the treadmill so it will stay in one place ONLY causeing foward force but not taking off. It can not go any faster than the treadmill because if whatever force the plane uses to be able to make it push ahead even one inch on the treadmill the treadmill will compensate and speed up to a point that is equal to what that plane needed to move ahead. Using only what is on it's side....gravity and friction (the treadmills side). So it will never move that inch or any at all foward.
Now...however the plane is still causeing air to be moved. through it's engines. At some point and some power of thrust the plane is going to be sucking so much air through that area that eventually it's going to cause the entire atmosphere to start moving and passing over it's wings also. At this point it will start to build up wind speed over it's wings. This will take an amazing amount of thrust and way above it's normal speed. At some point it will be fast enough to make the flaps usefull. At that second those flaps can give it some lift the plane will pull up and shoot foward with insane speed and rocket off that treadmill now that there is no more force pushing against it's wheels and causeing friction on the wheels, bearings etc (since it is no longer in contact with the treadmill at all). And it will be flying. Now it will be airborn and using air pressure and wind speed to keep it up.
Now if you have a prop plane this will happen much faster since the prop is in front of the flaps and pushing wind over the wings. Making the flaps usefull much sooner. But once it gets off the ground it will have to have enough force to propell it forward fast enough to catch enough air pressure to keep it up after it leaves the threadmill.
*some side notes*: A plane in space will NOT be able to take off (assuming it has air suppied to the jet fuel to ignite it). It would ONLY be able to move FORWARD. Flaps would be useless with no air in space unless postioned behind the engine thrust or the engine actually moved itself. This is why the plane would just sit there on a treadmill and not get lift at first. Thrust can push it foward it can't steer it.
*2nd note*: Put the plane on the treadmill. Start the treadmill.... what happens? It goes backward. Apply thust to keep it in one place. Then make the treadmill move faster.... the plane will now have to apply even more thrust to keep it from falling behind. So it does take power and thrust to compensate for the friction and gravity and whatnot. And that increases as the threadmill moves faster. I know it sounded bizzare at first but that guy that said the truck would just spin tires if pulling someone on a treadmill is correct. If that treadmill is moving 1000 MPH (random speed I chose) its going to be causeing an insane amount of pull back on that truck. The point in mentioning this is basicly that the faster the treadmill goes the more force back it will cause and if it can go to any speed it can match any force moving forward.
So in a way both sides are correct up to a point
What where you smoking?
Originally posted by: tk109
Here is what will happen:
So in a way both sides are correct up to a point
You have no idea how a plane actually flies do you?
mugs
Lifer
- Apr 29, 2003
- 48,920
- 46
- 91
This is the kind of response you get from a troll having a temper tantrum.
You seem to be intent on discussing the version of the problem that defies the laws of physics - and because the situation described in the problem cannot exist you take that to mean that it can't take off. On the contrary - how can you say if the plane would or would not take off if the situation it's supposed to take off in can't exist in the first place?
Even if you insist on using the poorly worded version of the problem, the answer is yes, the plane can still take off. A plane does not need to move relative to the ground in order to take off. You know how a plane has an airspeed and a ground speed? And they're not always the same? The airspeed is the one that matters, because that determines how much lift the wings generate. It doesn't matter what your groundspeed is, if you have a high enough airspeed the plane will leave the ground.
In other words - strong gust of wind.
But an intelligent person would use the version of the question that does not describe an impossible scenario. (That is, the version of the question where the treadmill matches the plane's speed relative to the ground, not the rotational speed of the wheels)
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