Moz - ur video went all high speed an Minie Mouyse halfway thru - was that deliberate? Anyway I too am geting wound up by people who have no real knowledge of physics talking about, "erm..maybe the wheels would jam" or "Man - that's like a zillion pounds of thrust -are you trying to tell me it gets no where?"
Some of the arguments you put forward aren't very enlightening although you are, of course, right about the bottom line. The plane will not take off.
The wording of the inital problem says that the speed of the treadmill magically matches that of the plane. Spurious though this setup may be, that is what we are given. Therefore the plane is not moving.
The only force that has any impact on whether a plane takes off is the only upwards force, the lift. Wings are a device for converting forward motion into upwards force (lift). If there is no forward motion, and the initial problem exactly states that there is none, then there is no lift. The plane will never take off.
The drive of a plane comes through its engines, not its wheels.
It wouldn't matter how fast the treadmill runs, that would only produce some slight friction on the wheels. The plane would however move forward due to the thrust of the engines and be able to reach a speed that allows it to take off.
If the planes engines are on, then they are moving air. if air is moving over the wings, then a force is generated. this force may not be enough to make it lift off, but i think that it cant be ignored. if the engine is on, and pulling air in the front, like all jets do, then the air it pulls in will be replaced by other air, creating a pressure difference SOMEWHERE around the plane. the plane may never fly or "take off", but i think those forces caused by changing air pressue should be looked at to fully understand the overall balance of force that this situation would generate.
The Plane WILL take off. Take some physics lessons.
The plane's wheels don't push it forward, the turbines do. The plane will go right off the treadmill. If you put an anti-gravity device underneath the plane and it floated in mid-air, would it still take off? Yes, because it's the turbines that push the air that propels the plane forward, regardless of wheels or anything holding it up.
however, you must allow that lift is based on airflow. should the treadmill cover enough area, eventually airfriction would force a 'convection' like current of air flow. this airflow over the wings should create the aforementioned lift. so, it depends on the size of the treadmill, and whether it can move air.
Yes moz is correct, if the plane is a jet or any type of plane with the thrust pushing the plane from the back. but the way any front propeller plane works is that the air is pulled from infront of it, and pushed over the wings, creating lift, thats it. so yes a front propeller plane would take off from the "treadmill". my email is megabass713@gmail.com, for any of you what would like to parry and repose.
Think about it: The plane ISN'T moving, just the tires are spinning. Kind of like when you're slipping on ice and you keep trying to regain your balance. Your legs might be moving like crazy but you're not moving. There is no wind flying by... Movement doesn't cause wind necessarily, moving through air causes wind.
Thus, as far as I can tell, there is no wind, pure and simply. "
CORRECT Now please STFU
Heh you skipped physics at school didn't you? Two equal and opposite forces cancelling each other out is not the same thing as "For every action there is an equal and opposite reaction". If you push a ball (action) you are also pushed back by the same amount and in the opposite direction (reaction). The reaction and action don't cancel each other out: if they did it would be impossible to do anything....
seriously, wrong.
if the belt were to be accelerated with a very small value the plane would role off the back. if there were a large acceleration it would be much like pulling the rug from under the dishes.
first of all, action reaction newtons 3rd law requires that the two forces involved be the same type. the treadmill force is a contact force and the thrust is not. the action reaction of the thrust is the air pushing back, this is how a jet works, please read, you know like the water rocket toys. the motion of the plane is determined by the net force.
get your friends together. get some rollerskates and a treadmill. then tie a rope to you around your waste. this is the thrust. tie one end to a car. turn on treadmill, you will find you stay stationary on the treadmill. no surprise. if you cut the rope you fall off the back. no surprise, just as the plane would. now lets turn up the thrust. this means drive the car btw. if you drive the car at the same speed you set the treadmill too, the car will go forward and you are tied to the car, what do you think happens? you go off the treadmill. now change the rope to a jet and see what happens. you will fly straight into a wall no matter what the treadmill speed is.
read a physics book before writing about action reaction. thanks
The air going into the engine and the thrust created are another action/reaction.
The two are independent from each other and therfore do not effect each other.
Since the treadmill speed and engine thrust do not effect each other, the plane will accelerate and take off prividede that the treadmill is long enough for the plane to build up the proper speed.
Now givin the nature of wheels/Bearings, the increased speed of the treadmill will have an effect on the planes speed, but not enough to prevent it from taking off.
How is it that the treadmill exerts any force on the plane at all? The brakes are off and the wheels turn freely. The treadmill cannot hold the airplane back against the force of the engines pushing it forward.
Moz, you are not answering the question though, just poininting out that the question is flawed.
And it is, no argument there.
However, the question does state that we have this magical treadmill that can prevent the plane from just accelerating off of the treadmill, and we have to work with that if we are to answer the question posed, as it is posed.
Its a stupid question, yes, and the treadmill would not work in real life, agreed! but there it is anyway, that magical treadmill, and it is the whole point of the question, and to simply state "the treadmill would not work, the plane would just drive off-of it and take off normally" is not answering the hypothetical situation created.
It would be the same as answering thouse typical math questions like "Train X drives 50 Mph, train Y 40 Mph, where do they collide?" with = They dont! in real life there are side tracks to prevent such stupid collisions!
Its true, but you'd get an F anyway, now woulden't you?
Yes the treadmill is stupid, and woulden't really work, but this hypothetical forces us to pretend that it does, its magic dude! woohoo! good, so what would happen?
Repeat after me: the treadmill has no influence on the thrust of the plane.
The thing goes like this: the plane isn't getting propulsion from its wheels, but from its engines (which act upon AIR). The wheel is just a movable part with no connection whatsoever on the thrust forward.
What moves a plane forward are its engines. If it were a car, then the treadmill would influence its movement, since a car gets its propulsion from the contact of its wheels with the ground. This is not the case with a plane.
The tread mill does not prevent forward motion of the plane. It spins in the opposite direction so if the plane is moving X mpg the treadmill is spining -X mph, and the wheels are spinning at -2X mph, but the wheels are spinning over the brearings! They spin dependent on the plane's motion relative to the treadmill.
The faster the plane moves froward, the faster the treadmill turns. As long as the bearings hold up to twice the normal rate of spin, it will fly.
I thought the problem was formulated as the speed of the runway is matched to the speed of the WHEELS, not plane itself. This means infinite wheels and treadmill speeds even if plane is moving slightly. Which make the whole problem stupid.
Well, I might be wrong, cba to find where this thing originated.
You can push theoretical model a bit closer to reality by assuming that plane wheels have mass and radius, thus having angular momentum that absorbs and stores all the power of the engines. They still will accelerate pretty fast in case of real-life-like parameters, but not _infinitely_ fast.
I have done all the math for this model once, and it's simple and sound, with no infinities whatsoever. So, if you assume that the statement in question is correct, you have at least one correct physical model that states "will not lift at least for some time, until wheels or threadmill explode due to the centrifugal forces".
if the plane cannot move forward. It will not take off.
What I am trying to get across is the plane WILL move forward, regardless of the treadmill's action.
The video was poorly formulated. I kind of did it as a one off quick vent of frustration and not as an all answering all knowing piece of scientific resource.
The plane will not move forward... You seem to be forgetting about gravity holding the plane to the treadmill. If the treadmill moves the plane moves, if the plane matches speed then the plane doesn't move in space.
By Moz's and your logic if the plane is not moving and the treadmill was running the plane won't move at all because you say it doesn't affect the plane itself but only the wheels.
You make a very vail point, once the venting is thrown aside. I admit that, at first, I simply assumed that plane would remain stationary. However, after some condsideration, and your passionately made point, I have reconsidered. Here is my understanding:
To grasp this problem you need to realize the fundemental difference between wheen propelled vehicles, like cars, bicycles, etc. and direct thrust vehclies, like, for instance, a turbojet aircraft or a jet truck. In a car, the is one constant speed between the wheels and the actually body of the car. If you're going 60 mph on the freeway, your wheels are also spinning at exactly 60 mph. It cannont be any other way. However, for direct thrust vehicles, like a jet truck or airplane, there are two speeds: The body of the craft itself, and the speed of the wheels. In all real world circumstances, these are equal, however, they do not have to be.
Now, lets look at our treadmill. It is currently going 0 mph. Now, we drop a 747-400 on it. It tops out at ~560 mph, and only needs to for ~200 to achieve liftoff. Our hypothetical captian throttles up, and now 4 turbojets are puting out ~280,000 pounds of thrust, and this big hunk of steel starts to roll foreward. Here is where it gets interesting. If we were to put a car in this situation, going one mile per hour, that car would role ~1.5 feet in 1 second. AS our treadmill matches wheel speed, it would go back ~1.5 feet, and the car would not move. Or 747, however, the wheels are able to simple move faster than the body. When the body is doing one mile an hour, the wheels are doing two, and so on. Obviously, we end up with some physical constraints, however, we simply choose to ignore those. Eventually the 747 reaches its takeoff velocity and lifts off, if the wheels havn't reached lightspeed, and become infinitely heavy.
If you put a skateboard on a treadmill that was going 5 mph and put a thruster on the skateboard that pushed the skateboard at 5 mph, are you saying that the skateboard would actually move forward? I don't understand the idea of a hovercraft on a treadmill. Doesn't a hovercraft hover? Isn't it just off the ground or barely touching the ground? Doesn't it have a force which moves it both up and forward? And put a rocket on a treadmill, would a rocket go anywhere? The forces remain at zero no matter what you do.
Think like this: stand on the ground next to the treadmill, with the skateboard on the mill. not put ONE foot on the skateboard. move it back and forwards as you like. see? it isnt really any harder to move it any direction, is it? thats how jet engines effect the airplane. it doesnt matter how the ground moves, as the plane is not propelled using the ground. Thats why those planes that land and take off of water only has those ski-things, and no water-propelled engines.. doesnt really matter which way the water flows, it doesnt use water to propel itself, like a boat does.
You are indeed correct... the plane could take off if the jet's engines could produce enough thrust to over come the friction of the tires rotation + provide enough forward momentum to reach the planes minimum take off speed.
the planes minimum take off speed is the value that it is because of the amount of air traveling around (over and below) the wing... not how fast it is going in relation to the ground. The wheels are not providing the thrust as the poster above has stated.
Here is an example. There are two planes, one on a "treadmill" and one on a normal runway, sitting side by side. Since both planes are using the same atmosphere to take off they will both attain the same speed and take off at the same distance from the starting point. The only difference is that the plane on the treadmill will have it's wheels spinning at a much higher rate of speed.
ALL OF THE PEOPLE ON THIS FORUM WHO ARE SAYING "Equal and opposite actions/reactions" obviously do not have the ability to picture these forces in their head.
WHY?
Because both the treadmill and the forward thrust from the jet engines have an ADDITIVE force. Think about it... Both the tread mill and the engines are causing the wheels to spin IN THE SAME DIRECTION. If the treadmil is moving towards the rear of the plane, the wheels will be spinning forward. If the engines thrust is pushing towards the rear of the plane the wheels will be spinning forward. What does this mean? This means that the only difference between a plane on a normal runway and one on the tread mill will be the speed of the wheels. Everyone knows that free spinning wheels are their OWN seperate system... and the physics and forces on those wheels cannot be applied to the plane... unless talking about forces that would be transfered up the supporting structure of the landing gear. If you do transfer any of the centrifugal energies to the plane, you are suggesting there is some sort of energy transfer (outside of friction) to the landing gear... which would NOT be free spinning wheels.
Comments
Moz - ur video went all high
Moz - ur video went all high speed an Minie Mouyse halfway thru - was that deliberate? Anyway I too am geting wound up by people who have no real knowledge of physics talking about, "erm..maybe the wheels would jam" or "Man - that's like a zillion pounds of thrust -are you trying to tell me it gets no where?"
Some of the arguments you put forward aren't very enlightening although you are, of course, right about the bottom line. The plane will not take off.
The wording of the inital problem says that the speed of the treadmill magically matches that of the plane. Spurious though this setup may be, that is what we are given. Therefore the plane is not moving.
The only force that has any impact on whether a plane takes off is the only upwards force, the lift. Wings are a device for converting forward motion into upwards force (lift). If there is no forward motion, and the initial problem exactly states that there is none, then there is no lift. The plane will never take off.
The Plane Can Take
The Plane Can Take Off!!!
The drive of a plane comes through its engines, not its wheels.
It wouldn't matter how fast the treadmill runs, that would only produce some slight friction on the wheels. The plane would however move forward due to the thrust of the engines and be able to reach a speed that allows it to take off.
Sir, I believe you have a
Sir, I believe you have a problem with your brain not working.
If the planes engines are
If the planes engines are on, then they are moving air. if air is moving over the wings, then a force is generated. this force may not be enough to make it lift off, but i think that it cant be ignored. if the engine is on, and pulling air in the front, like all jets do, then the air it pulls in will be replaced by other air, creating a pressure difference SOMEWHERE around the plane. the plane may never fly or "take off", but i think those forces caused by changing air pressue should be looked at to fully understand the overall balance of force that this situation would generate.
"The plane will not take
"The plane will not take off"
The Plane WILL take off. Take some physics lessons.
The plane's wheels don't push it forward, the turbines do. The plane will go right off the treadmill. If you put an anti-gravity device underneath the plane and it floated in mid-air, would it still take off? Yes, because it's the turbines that push the air that propels the plane forward, regardless of wheels or anything holding it up.
however, you must allow that
however, you must allow that lift is based on airflow. should the treadmill cover enough area, eventually airfriction would force a 'convection' like current of air flow. this airflow over the wings should create the aforementioned lift. so, it depends on the size of the treadmill, and whether it can move air.
Yes moz is correct, if the
Yes moz is correct, if the plane is a jet or any type of plane with the thrust pushing the plane from the back. but the way any front propeller plane works is that the air is pulled from infront of it, and pushed over the wings, creating lift, thats it. so yes a front propeller plane would take off from the "treadmill". my email is megabass713@gmail.com, for any of you what would like to parry and repose.
QUOTE COOLDAWG" I still
QUOTE COOLDAWG"
I still don't agree. Think
I still don't agree.
Think about it: The plane ISN'T moving, just the tires are spinning. Kind of like when you're slipping on ice and you keep trying to regain your balance. Your legs might be moving like crazy but you're not moving. There is no wind flying by... Movement doesn't cause wind necessarily, moving through air causes wind.
Thus, as far as I can tell, there is no wind, pure and simply. "
CORRECT Now please STFU
Newton's third law. For
Newton's third law.
For every action there is an equal and opposite reaction.
Both the jet, and the belt are actions. That are equal, yet opposite. Therefore nothing happens because both neutralize the other.
Heh you skipped physics at
Heh you skipped physics at school didn't you? Two equal and opposite forces cancelling each other out is not the same thing as "For every action there is an equal and opposite reaction". If you push a ball (action) you are also pushed back by the same amount and in the opposite direction (reaction). The reaction and action don't cancel each other out: if they did it would be impossible to do anything....
seriously, wrong. if the
seriously, wrong.
if the belt were to be accelerated with a very small value the plane would role off the back. if there were a large acceleration it would be much like pulling the rug from under the dishes.
first of all, action reaction newtons 3rd law requires that the two forces involved be the same type. the treadmill force is a contact force and the thrust is not. the action reaction of the thrust is the air pushing back, this is how a jet works, please read, you know like the water rocket toys. the motion of the plane is determined by the net force.
get your friends together. get some rollerskates and a treadmill. then tie a rope to you around your waste. this is the thrust. tie one end to a car. turn on treadmill, you will find you stay stationary on the treadmill. no surprise. if you cut the rope you fall off the back. no surprise, just as the plane would. now lets turn up the thrust. this means drive the car btw. if you drive the car at the same speed you set the treadmill too, the car will go forward and you are tied to the car, what do you think happens? you go off the treadmill. now change the rope to a jet and see what happens. you will fly straight into a wall no matter what the treadmill speed is.
read a physics book before writing about action reaction. thanks
***You are wrong*** The
***You are wrong***
The wheels and the belt are one action/re-action.
The air going into the engine and the thrust created are another action/reaction.
The two are independent from each other and therfore do not effect each other.
Since the treadmill speed and engine thrust do not effect each other, the plane will accelerate and take off prividede that the treadmill is long enough for the plane to build up the proper speed.
Now givin the nature of wheels/Bearings, the increased speed of the treadmill will have an effect on the planes speed, but not enough to prevent it from taking off.
You are the Cage Monkey's
You are the Cage Monkey's Leader. Worst application of Newton's Third Law ever.
The engine and treadmill are not equal and opposing actions.
Not equal and opposite
How is it that the treadmill exerts any force on the plane at all? The brakes are off and the wheels turn freely. The treadmill cannot hold the airplane back against the force of the engines pushing it forward.
Moz, you are not answering
Moz, you are not answering the question though, just poininting out that the question is flawed.
And it is, no argument there.
However, the question does state that we have this magical treadmill that can prevent the plane from just accelerating off of the treadmill, and we have to work with that if we are to answer the question posed, as it is posed.
Its a stupid question, yes, and the treadmill would not work in real life, agreed! but there it is anyway, that magical treadmill, and it is the whole point of the question, and to simply state "the treadmill would not work, the plane would just drive off-of it and take off normally" is not answering the hypothetical situation created.
It would be the same as answering thouse typical math questions like "Train X drives 50 Mph, train Y 40 Mph, where do they collide?" with = They dont! in real life there are side tracks to prevent such stupid collisions!
Its true, but you'd get an F anyway, now woulden't you?
Yes the treadmill is stupid, and woulden't really work, but this hypothetical forces us to pretend that it does, its magic dude! woohoo! good, so what would happen?
Repeat after me: the
Repeat after me: the treadmill has no influence on the thrust of the plane.
The thing goes like this: the plane isn't getting propulsion from its wheels, but from its engines (which act upon AIR). The wheel is just a movable part with no connection whatsoever on the thrust forward.
What moves a plane forward are its engines. If it were a car, then the treadmill would influence its movement, since a car gets its propulsion from the contact of its wheels with the ground. This is not the case with a plane.
You miss-read the problem
The tread mill does not prevent forward motion of the plane. It spins in the opposite direction so if the plane is moving X mpg the treadmill is spining -X mph, and the wheels are spinning at -2X mph, but the wheels are spinning over the brearings! They spin dependent on the plane's motion relative to the treadmill.
The faster the plane moves froward, the faster the treadmill turns. As long as the bearings hold up to twice the normal rate of spin, it will fly.
I thought the problem was
I thought the problem was formulated as the speed of the runway is matched to the speed of the WHEELS, not plane itself. This means infinite wheels and treadmill speeds even if plane is moving slightly. Which make the whole problem stupid.
Well, I might be wrong, cba to find where this thing originated.
if the "theoretical" weels
if the "theoretical" weels will not blowup, they will develop a speed of light and become unmovable, sorry about you brain man.
You can push theoretical
You can push theoretical model a bit closer to reality by assuming that plane wheels have mass and radius, thus having angular momentum that absorbs and stores all the power of the engines. They still will accelerate pretty fast in case of real-life-like parameters, but not _infinitely_ fast.
I have done all the math for this model once, and it's simple and sound, with no infinities whatsoever. So, if you assume that the statement in question is correct, you have at least one correct physical model that states "will not lift at least for some time, until wheels or threadmill explode due to the centrifugal forces".
The plane at 0 degrees there
The plane at 0 degrees there would be no action, at 5 degrees it would take off.
if the plane cannot move
if the plane cannot move forward. It will not take off.
What I am trying to get across is the plane WILL move forward, regardless of the treadmill's action.
The video was poorly formulated. I kind of did it as a one off quick vent of frustration and not as an all answering all knowing piece of scientific resource.
The plane will not move
The plane will not move forward... You seem to be forgetting about gravity holding the plane to the treadmill. If the treadmill moves the plane moves, if the plane matches speed then the plane doesn't move in space.
By Moz's and your logic if the plane is not moving and the treadmill was running the plane won't move at all because you say it doesn't affect the plane itself but only the wheels.
You make a very vail point,
You make a very vail point, once the venting is thrown aside. I admit that, at first, I simply assumed that plane would remain stationary. However, after some condsideration, and your passionately made point, I have reconsidered. Here is my understanding:
To grasp this problem you need to realize the fundemental difference between wheen propelled vehicles, like cars, bicycles, etc. and direct thrust vehclies, like, for instance, a turbojet aircraft or a jet truck. In a car, the is one constant speed between the wheels and the actually body of the car. If you're going 60 mph on the freeway, your wheels are also spinning at exactly 60 mph. It cannont be any other way. However, for direct thrust vehicles, like a jet truck or airplane, there are two speeds: The body of the craft itself, and the speed of the wheels. In all real world circumstances, these are equal, however, they do not have to be.
Now, lets look at our treadmill. It is currently going 0 mph. Now, we drop a 747-400 on it. It tops out at ~560 mph, and only needs to for ~200 to achieve liftoff. Our hypothetical captian throttles up, and now 4 turbojets are puting out ~280,000 pounds of thrust, and this big hunk of steel starts to roll foreward. Here is where it gets interesting. If we were to put a car in this situation, going one mile per hour, that car would role ~1.5 feet in 1 second. AS our treadmill matches wheel speed, it would go back ~1.5 feet, and the car would not move. Or 747, however, the wheels are able to simple move faster than the body. When the body is doing one mile an hour, the wheels are doing two, and so on. Obviously, we end up with some physical constraints, however, we simply choose to ignore those. Eventually the 747 reaches its takeoff velocity and lifts off, if the wheels havn't reached lightspeed, and become infinitely heavy.
-Drew K.
Of curse the plane will
Of curse the plane will never move. Actually, that's exactly why hovercrafts don't move and rockets never take off either... ;)
If you put a skateboard on a
If you put a skateboard on a treadmill that was going 5 mph and put a thruster on the skateboard that pushed the skateboard at 5 mph, are you saying that the skateboard would actually move forward? I don't understand the idea of a hovercraft on a treadmill. Doesn't a hovercraft hover? Isn't it just off the ground or barely touching the ground? Doesn't it have a force which moves it both up and forward? And put a rocket on a treadmill, would a rocket go anywhere? The forces remain at zero no matter what you do.
Think like this: stand on
Think like this: stand on the ground next to the treadmill, with the skateboard on the mill. not put ONE foot on the skateboard. move it back and forwards as you like. see? it isnt really any harder to move it any direction, is it? thats how jet engines effect the airplane. it doesnt matter how the ground moves, as the plane is not propelled using the ground. Thats why those planes that land and take off of water only has those ski-things, and no water-propelled engines.. doesnt really matter which way the water flows, it doesnt use water to propel itself, like a boat does.
i meant "now put ONE foot...
i meant "now put ONE foot... blahblha"
You are indeed correct...
You are indeed correct... the plane could take off if the jet's engines could produce enough thrust to over come the friction of the tires rotation + provide enough forward momentum to reach the planes minimum take off speed.
the planes minimum take off speed is the value that it is because of the amount of air traveling around (over and below) the wing... not how fast it is going in relation to the ground. The wheels are not providing the thrust as the poster above has stated.
Here is an example. There are two planes, one on a "treadmill" and one on a normal runway, sitting side by side. Since both planes are using the same atmosphere to take off they will both attain the same speed and take off at the same distance from the starting point. The only difference is that the plane on the treadmill will have it's wheels spinning at a much higher rate of speed.
ALL OF THE PEOPLE ON THIS FORUM WHO ARE SAYING "Equal and opposite actions/reactions" obviously do not have the ability to picture these forces in their head.
WHY?
Because both the treadmill and the forward thrust from the jet engines have an ADDITIVE force. Think about it... Both the tread mill and the engines are causing the wheels to spin IN THE SAME DIRECTION. If the treadmil is moving towards the rear of the plane, the wheels will be spinning forward. If the engines thrust is pushing towards the rear of the plane the wheels will be spinning forward. What does this mean? This means that the only difference between a plane on a normal runway and one on the tread mill will be the speed of the wheels. Everyone knows that free spinning wheels are their OWN seperate system... and the physics and forces on those wheels cannot be applied to the plane... unless talking about forces that would be transfered up the supporting structure of the landing gear. If you do transfer any of the centrifugal energies to the plane, you are suggesting there is some sort of energy transfer (outside of friction) to the landing gear... which would NOT be free spinning wheels.
YES THE PLANE WOULD TAKE OFF.
Speaking of skateboards -
Speaking of skateboards - long ago when this riddle came out, I used a skateboarding on a treadmill as an explanation for why the plane takes off.
http://www.michaelbuffington.com/articles/2006/02/09/conveyor-belts-airp...