Can the airplane take off?

[BrownTown]

I like how the fool asks someone to prove his equations wrong and 3 people promptly respond and proove him wrong, this is good to see . Also, about the 1=2 thing, that is another good one to confuse people. I don't really like these tricky things though, becasue they are mostly just bait to get people to bite at and say the wrong answer so you can tell them they are wrong and stoke your ego . Of course, SOME people here refuse to admit they are wrong even after the facts are presented, so you end up just getting 5 pages of worthless posts...

EDIT: lol, and now I just extended it to 6 pages of worthlessness.

 

[sao123]

Originally posted by: smack Down
The size of the force doesn't matter or where it comes from doesn't matter if you read the question such that the speed of the treadmill tracks the speed of the plane relitive to the treadmill surface you get this equation. This is the case most people think about when talking about treadmills

i just wanted to point out a further error.


Your argument now has a paradox, a situation as you will see that can never exist...
If the plane moves forward at 300 MPH, then its wheels will do likewise, and the treadmill will go 300 MPH backward. But if the treadmill is going 300 MPH backward, then the wheels are really turning 600 MPH forward. But if the wheels are going 600 MPH forward, then in order to make the plane stationary, the treadmill must have been running at 600mph all along to match the forweard velocity of the wheels. But you already defined that the treadmill was going 300mph.

Utter Nonsense. The question thus stated asks the impossible -- simply put, that V = V + 300 a statement we know to be false. Your own question contradicts itself.

 

[smack Down]

define Vt = Vp_g through the problem statement "when the airplane moves forward, the conveyor matches its speed" NOT Vt = -Vp_t as you stated ........it does not say when the airplane moves forward with respect to treadmill, it just says moves forward.

Right the problem doesn't give a frame of reference for the speed of the treadmill. So to assume the reference is to the surface of the treadmill is just a valid as to assume ground.

 

[smack Down]

Originally posted by: sao123

Originally posted by: smack Down

Originally posted by: AeroEngy

Originally posted by: smack Down
The size of the force doesn't matter or where it comes from doesn't matter if you read the question such that the speed of the treadmill tracks the speed of the plane relitive to the treadmill surface you get this equation. This is the case most people think about when talking about treadmills

VPlane to treadmill = Vground + -Vtreadmill
Now by definition of the problem Vtreadmill = -VplanetoTreadmill
We get Vtreadmill = -Vground + Vtreadmill
Therefor Vground = 0 and the plane doesn't take off.

I know I said that my previous post was going to be my last. But LMAO ... are you realling trying to argue that size and direction of the forces don't matter. When they are the only thing that matters.

Newton's Second Law of motion- The rate of change of the momentum of a body is directly proportional to the net force acting on it, and the direction of the change in momentum takes place in the direction of the net force.

Just show how my equations are wroung. It is simple algebra how or why it happens doesn't matter because the question defines it as happening.

Did you read my last post with diagram?

The plane will take off.

Jet engines provide thrust relative to the atmosphere... not relative to the ground.

The question does not and can not define things happening as you have described them. Its impossible.
Your equations are wrong because they dont have a common frame of reference:
You must have the common frame of reference the "ATMOSPHERE."

Velocity of the plane to the ground = (VplanetoATM - VGroundtoATM)
= (+300 + 0) = 300
Velocity of the Treadmill to the ground = (VGroundtoATM - VTreadtoATM)
= (0 - 300) = -300
Velocity of the plane to the Treadmills = (VPlanetoATM - VTreadtoATM)
= (300 - -300) = 600

There is no physical way for the engines to be on and the plane not be moving forward because the engines push against the atmosphere, not the ground. Yuor equations dont even have the atmosphere in them as a reference point.

Again you can pick any frame of reference one is not more valid then the other. The surface of the treadmill is my frame of reference for defining the speed of an airplane. The question doesn't define speed so it is left up to the read to interrupt the defintion of speed.

 

[smack Down]

Originally posted by: sao123

Originally posted by: smack Down
The size of the force doesn't matter or where it comes from doesn't matter if you read the question such that the speed of the treadmill tracks the speed of the plane relitive to the treadmill surface you get this equation. This is the case most people think about when talking about treadmills

i just wanted to point out a further error.


Your argument now has a paradox, a situation as you will see that can never exist...
If the plane moves forward at 300 MPH, then its wheels will do likewise, and the treadmill will go 300 MPH backward. But if the treadmill is going 300 MPH backward, then the wheels are really turning 600 MPH forward. But if the wheels are going 600 MPH forward, then in order to make the plane stationary, the treadmill must have been running at 600mph all along to match the forweard velocity of the wheels. But you already defined that the treadmill was going 300mph.

Utter Nonsense. The question thus stated asks the impossible -- simply put, that V = V + 300 a statement we know to be false. Your own question contradicts itself.

No it doesn't the speed of the plane isn't fixed as the treadmill speeds up the speed of the plane will approach zero and the treadmill will reach a steady state.

 

[sao123]

Originally posted by: smack Down

Again you can pick any frame of reference one is not more valid then the other. The surface of the treadmill is my frame of reference for defining the speed of an airplane. The question doesn't define speed so it is left up to the read to interrupt the defintion of speed.

I have 3 questions:
So then if what you say is true...Is the plane pushing the entire atmosphere backwards to match the speed of the treadmill?

Originally posted by: smack Down

No it doesn't the speed of the plane isn't fixed as the treadmill speeds up the speed of the plane will approach zero and the treadmill will reach a steady state.

Explain how the conveyor belt is actually moving the plane backwards, instead of just rotating the wheels freely?



Finally, I want to know if a plane can take off on a runway pointing due west?

 

[gsellis]

You cannot see that any V change in the treadmill only delta Vs at the wheel and not at the axle. If the resistance at the hub of the wheel is 0, there is NO, 0, ZERO, force on the airplane. All the force generated by the treadmill just creates acceleration in the wheel, thus increasing the wheels V, but not the airplane. Adding some resistance, does retard the plane slightly because the friction will make the wheel resist matching the force generated by the treadmill. But, the force of the engine on the airplane easily overcomes any such resistance. Now if you move the treadmill too, you just get a path of destruction until the plane is in the air.

 

[smack Down]

Originally posted by: gsellis
You cannot see that any V change in the treadmill only delta Vs at the wheel and not at the axle. If the resistance at the hub of the wheel is 0, there is NO, 0, ZERO, force on the airplane. All the force generated by the treadmill just creates acceleration in the wheel, thus increasing the wheels V, but not the airplane. Adding some resistance, does retard the plane slightly because the friction will make the wheel resist matching the force generated by the treadmill. But, the force of the engine on the airplane easily overcomes any such resistance. Now if you move the treadmill too, you just get a path of destruction until the plane is in the air.

Friction in the wheel doesn't matter.

A rolling wheel will push on its axle. THis will apply a force to the whole plane. If a wheel rolls backwards by 2 feet the plane must also roll backwards by 2 feet.

 

[brikis98]

Originally posted by: smack Down

Originally posted by: gsellis
You cannot see that any V change in the treadmill only delta Vs at the wheel and not at the axle. If the resistance at the hub of the wheel is 0, there is NO, 0, ZERO, force on the airplane. All the force generated by the treadmill just creates acceleration in the wheel, thus increasing the wheels V, but not the airplane. Adding some resistance, does retard the plane slightly because the friction will make the wheel resist matching the force generated by the treadmill. But, the force of the engine on the airplane easily overcomes any such resistance. Now if you move the treadmill too, you just get a path of destruction until the plane is in the air.

Friction in the wheel doesn't matter.

A rolling wheel will push on its axle. THis will apply a force to the whole plane. If a wheel rolls backwards by 2 feet the plane must also roll backwards by 2 feet.

you have it backwards. the wheel SPINS from the treadmill. it doesn't roll (minus the tiny effects from friction/torque).

on the other hand the axle of the plane, propelled by the jet engines, pushes the wheel. that causes it to roll forward.

compare me holding my rollerblades over a treadmill - the wheels spin, but it doesn't move. then, when i push them forward, they wheels actually roll.

 

[smack Down]

Originally posted by: brikis98

Originally posted by: smack Down

Originally posted by: gsellis
You cannot see that any V change in the treadmill only delta Vs at the wheel and not at the axle. If the resistance at the hub of the wheel is 0, there is NO, 0, ZERO, force on the airplane. All the force generated by the treadmill just creates acceleration in the wheel, thus increasing the wheels V, but not the airplane. Adding some resistance, does retard the plane slightly because the friction will make the wheel resist matching the force generated by the treadmill. But, the force of the engine on the airplane easily overcomes any such resistance. Now if you move the treadmill too, you just get a path of destruction until the plane is in the air.

Friction in the wheel doesn't matter.

A rolling wheel will push on its axle. THis will apply a force to the whole plane. If a wheel rolls backwards by 2 feet the plane must also roll backwards by 2 feet.

you have it backwards. the wheel SPINS from the treadmill. it doesn't roll (minus the tiny effects from friction/torque).

on the other hand the axle of the plane, propelled by the jet engines, pushes the wheel. that causes it to roll forward.

compare me holding my rollerblades over a treadmill - the wheels spin, but it doesn't move. then, when i push them forward, they wheels actually roll.

You holding the rollerblades in place applies more force the threadmill if you where to hold it with less force it would roll backwards.

 

[AeroEngy]

Originally posted by: smack Down

define Vt = Vp_g through the problem statement "when the airplane moves forward, the conveyor matches its speed" NOT Vt = -Vp_t as you stated ........it does not say when the airplane moves forward with respect to treadmill, it just says moves forward.

Right the problem doesn't give a frame of reference for the speed of the treadmill. So to assume the reference is to the surface of the treadmill is just a valid as to assume ground.

So by your own logic above IF both reference frames are equally valid then with my definition Vp_g is not restricted to 0.

I am still waiting on you to try to refute where I showed that the sum of the forces were non-zero thus accelerating the plane with respect to the ground. Show me with proof that the treadmill can exert a force equal to the thrust from an airplane. All the equations that you or I make up are not proven. Lets just stick with the laws of physics and proven equations of motion.

My guess is that you are arguing for the sake of arguing. I am hoping you aren't dumb enough to actually think that the forces exerted and friction don't matter in in a dynamics problem.

 

[BrownTown]

Ok, look, if there is no friction in the wheels, the speed of the conveyer and the speed of the plane are 100% independant. That means that if you took the plane and sat it down on a treadmill going 1000mph the plane would not move 1mm relative to the ground, the wheels would simply be rotating really fast, and all the energy has come from the treadmill, not the fuel in the plane. I know it sounds odd, but it is truth.

I am still not sure whether you simply don't get it, or whether you do understand, but are being stubborn and trying to save faith. I think the latter is more likely correct, but all you are doing is making people think you are more and more of a fool. It is NOT equally valid for you to misinterpret the problem. Your interpretation is WRONG, it is not what the designer of the problem wanted you to think. Personally, I think this thread should be closed as rapidly as possible. Also, not speakign for anyone else, but each further psot you make losses you respect in my eyes personally, and very possibly in the eyes of many others. I know I'm sorta being an ass about that, but it is the truth. And hopefully it will get this thread clsoed quicker if I make an admin mad .

EDIT: if you wan't to actually convince anyone, draw the freebody diagrams of the forces acting on the wheels, and on the rest of the plane, I'll do it for you in about 5 hours after lab, but if you do it first it will look cool and prove me right .

 

[dkozloski]

How about another variable to increase confusion. A good many aircraft have sufficient thrust to slide the wheels with the brakes locked to a degree sufficient to allow the aircraft to take off. A DC-8 with a load of cattle headed for Japan did precisely this years ago while attempting a takeoff in Anchorage, Alaska. It cleared the ground but flew into terrain later. On that basis empirical evidence is that the conveyor belt movement is irrelevant.

 

[brikis98]

Originally posted by: smack Down

Originally posted by: brikis98

Originally posted by: smack Down

Originally posted by: gsellis
You cannot see that any V change in the treadmill only delta Vs at the wheel and not at the axle. If the resistance at the hub of the wheel is 0, there is NO, 0, ZERO, force on the airplane. All the force generated by the treadmill just creates acceleration in the wheel, thus increasing the wheels V, but not the airplane. Adding some resistance, does retard the plane slightly because the friction will make the wheel resist matching the force generated by the treadmill. But, the force of the engine on the airplane easily overcomes any such resistance. Now if you move the treadmill too, you just get a path of destruction until the plane is in the air.

Friction in the wheel doesn't matter.

A rolling wheel will push on its axle. THis will apply a force to the whole plane. If a wheel rolls backwards by 2 feet the plane must also roll backwards by 2 feet.

you have it backwards. the wheel SPINS from the treadmill. it doesn't roll (minus the tiny effects from friction/torque).

on the other hand the axle of the plane, propelled by the jet engines, pushes the wheel. that causes it to roll forward.

compare me holding my rollerblades over a treadmill - the wheels spin, but it doesn't move. then, when i push them forward, they wheels actually roll.

You holding the rollerblades in place applies more force the threadmill if you where to hold it with less force it would roll backwards.

you're just being stubborn now. you must realize that the force with which the rollerblades (and airplane) are being pushed from is:

1. relatively small (especially compared to me pushing the rollerblade or a jet engine pushing the plane)
2. are from friction (bearings are not perfect) and torque (spinning wheel)
3. are NOT the same as with a car, where the wheels are connected to a drive train?

let's think of a very similar scenario. we again have me holding a rollerblade on a treadmill, but this time, the bearings of the rollerblade are very clogged/rusty to the point where the wheels can't spin.

1. do you agree that i'd have to apply MUCH more force to keep the rollerblade on that same treadmill?
2. if so, do you agree that if the bearings were slighly less dirty/rusty, allowing the wheel to spin a bit, i'd have to apply less and less force to keep the rollerblade there?
3. and finally, if we extend this to a (nearly) friction free environment, do you agree that i'd have to apply almost NO force to keep the rollerblade there?

if you have any reason in your mind, you should agree with the above 3 statements. in which case, you should make the final connection that the airplane is exactly analogous and that the treadmill will provide almost no resistance to the plane moving forward and becoming airborne.

 

[dkozloski]

As a practcal matter. Once the wheel starts to slide on the belt the coefficient of friction goes nearly to zero. Witness what happens to the motion of a dragster during a burnout. The faster the belt goes in reverse the less traction it provides. The plane is going to fly whether you want it to or not.

 

[sao123]

Originally posted by: smack Down
Friction in the wheel doesn't matter.

A rolling wheel will push on its axle. THis will apply a force to the whole plane. If a wheel rolls backwards by 2 feet the plane must also roll backwards by 2 feet.

You failed to answer my 3 bolded questions.

 

[randay]

Originally posted by: smack Down
Depends if the treadmill tracks the speed of the plane relitive to ground then it takes off or if the treadmill tracks the speed of the plane relitive to treadmill's surface then it does not.

Wrong, that doesn't matter at all. The plane still takes off. The only difference in those two situations is that when the treadmil tracks the speed of the plane relative to the treadmills surface the treadmill and the planes wheels will be moving exponentially(infinitely?) faster then it would if the treadmill tracks the planes speed relative to the ground.

In fact, the treadmill tracking the plane relative to the treadmills surface is quite impossible. The treadmills own actions would effect its reading and it would accelerate indefinately and infinitely even after the plane takes off, which it will.

for example, the plane moves 1 mph, the mill moves 1mph, the plane is now moving 2 mph relative to the mill. The plane moves 1mph, the mill moves 2mph, the plane is now moving 3 mphs relative to the mill. and so on and so forth until infinity?

 

[smack Down]

for example, the plane moves 1 mph, the mill moves 1mph, the plane is now moving 2 mph relative to the mill. The plane moves 1mph, the mill moves 2mph, the plane is now moving 3 mphs relative to the mill. and so on and so forth until infinity?

It only goes towards infinity if you assume that the treadmill can't effect the plane. Which is wrong because the treadmill applies torque to the plane.

 

[sao123]

Originally posted by: smack Down

for example, the plane moves 1 mph, the mill moves 1mph, the plane is now moving 2 mph relative to the mill. The plane moves 1mph, the mill moves 2mph, the plane is now moving 3 mphs relative to the mill. and so on and so forth until infinity?

It only goes towards infinity if you assume that the treadmill can't effect the plane. Which is wrong because the treadmill applies torque to the plane.

Still avoiding my questions I see.

 

[smack Down]

Originally posted by: brikis98

Originally posted by: smack Down

Originally posted by: brikis98

Originally posted by: smack Down

Originally posted by: gsellis
You cannot see that any V change in the treadmill only delta Vs at the wheel and not at the axle. If the resistance at the hub of the wheel is 0, there is NO, 0, ZERO, force on the airplane. All the force generated by the treadmill just creates acceleration in the wheel, thus increasing the wheels V, but not the airplane. Adding some resistance, does retard the plane slightly because the friction will make the wheel resist matching the force generated by the treadmill. But, the force of the engine on the airplane easily overcomes any such resistance. Now if you move the treadmill too, you just get a path of destruction until the plane is in the air.

Friction in the wheel doesn't matter.

A rolling wheel will push on its axle. THis will apply a force to the whole plane. If a wheel rolls backwards by 2 feet the plane must also roll backwards by 2 feet.

you have it backwards. the wheel SPINS from the treadmill. it doesn't roll (minus the tiny effects from friction/torque).

on the other hand the axle of the plane, propelled by the jet engines, pushes the wheel. that causes it to roll forward.

compare me holding my rollerblades over a treadmill - the wheels spin, but it doesn't move. then, when i push them forward, they wheels actually roll.

You holding the rollerblades in place applies more force the threadmill if you where to hold it with less force it would roll backwards.

you're just being stubborn now. you must realize that the force with which the rollerblades (and airplane) are being pushed from is:

1. relatively small (especially compared to me pushing the rollerblade or a jet engine pushing the plane)
2. are from friction (bearings are not perfect) and torque (spinning wheel)
3. are NOT the same as with a car, where the wheels are connected to a drive train?

let's think of a very similar scenario. we again have me holding a rollerblade on a treadmill, but this time, the bearings of the rollerblade are very clogged/rusty to the point where the wheels can't spin.

1. do you agree that i'd have to apply MUCH more force to keep the rollerblade on that same treadmill?
2. if so, do you agree that if the bearings were slighly less dirty/rusty, allowing the wheel to spin a bit, i'd have to apply less and less force to keep the rollerblade there?
3. and finally, if we extend this to a (nearly) friction free environment, do you agree that i'd have to apply almost NO force to keep the rollerblade there?

if you have any reason in your mind, you should agree with the above 3 statements. in which case, you should make the final connection that the airplane is exactly analogous and that the treadmill will provide almost no resistance to the plane moving forward and becoming airborne.

Assuming by frictionless you are talking about the wheel and the axle then no. You don't feel much force because you wheels are so small. Go put a car tire on and you will have a very hard time keep it on the treadmill because there is much more torque applied to the wheel.

 

[MrPickins]

Originally posted by: smack Down
Assume by frictionless you are talking about the wheel and the axle then no. You don't feel much force because you wheels are so small. Go put a car tire on and you will have a very hard time keep it on the treadmill because there is much more torque applied to the wheel.

People can't apply the amount of force a few jet engines can.

Hence, the scaled down model.

 

[smack Down]

Originally posted by: MrPickins

Originally posted by: smack Down
Assume by frictionless you are talking about the wheel and the axle then no. You don't feel much force because you wheels are so small. Go put a car tire on and you will have a very hard time keep it on the treadmill because there is much more torque applied to the wheel.

People can't apply the amount of force a few jet engines can.

Hence, the scaled down model.

And a treadmill can't go infinitly fast. The guy thinks friction is the force that matter it is not torque is what matters.

 

[MrPickins]

Originally posted by: smack Down

Originally posted by: MrPickins

Originally posted by: smack Down
Assume by frictionless you are talking about the wheel and the axle then no. You don't feel much force because you wheels are so small. Go put a car tire on and you will have a very hard time keep it on the treadmill because there is much more torque applied to the wheel.

People can't apply the amount of force a few jet engines can.

Hence, the scaled down model.

And a treadmill can't go infinitly fast. The guy thinks friction is the force that matter it is not torque is what matters.

But you still think that this torque applies more force to the axle than the plane's engines can.

Prove it.

 

[smack Down]

Originally posted by: MrPickins

Originally posted by: smack Down

Originally posted by: MrPickins

Originally posted by: smack Down
Assume by frictionless you are talking about the wheel and the axle then no. You don't feel much force because you wheels are so small. Go put a car tire on and you will have a very hard time keep it on the treadmill because there is much more torque applied to the wheel.

People can't apply the amount of force a few jet engines can.

Hence, the scaled down model.

And a treadmill can't go infinitly fast. The guy thinks friction is the force that matter it is not torque is what matters.

But you still think that this torque applies more force to the axle than the plane's engines can.

Prove it.

Lets see if you can follow, one more time for all the people who failed physics.

Let talk about why a plane wheel spins in the first place lets use assume a perfect wheel that never slips and an axle that has no friction.

1. The rotation of the wheel is porportional to the speed of the plane. Do you agree that this is the case. This is a by product of the fact that the wheel never slips. If the plane goes from point A to point B the wheel must have rolled that same distance.

2. 1 works in the other direction the speed of the plane is portional to speed of the wheels because again the wheels don't slip. The wheels roll over the same distance the plane does.

But don't take my word for it just go outside and put your car in neutral and push it. Watch as the wheels move. Now try spinng on of the wheel backwards and watch the car go backwards.

Ok, so now you should understand how a wheel works.

For the plane not to have forward motion all the treadmill has to do is rotate the wheels backwards at a speed greater the plane is rotating them forwards.

 

[MrPickins]

Originally posted by: smack Down

Originally posted by: MrPickins

Originally posted by: smack Down

Originally posted by: MrPickins

Originally posted by: smack Down
Assume by frictionless you are talking about the wheel and the axle then no. You don't feel much force because you wheels are so small. Go put a car tire on and you will have a very hard time keep it on the treadmill because there is much more torque applied to the wheel.

People can't apply the amount of force a few jet engines can.

Hence, the scaled down model.

And a treadmill can't go infinitly fast. The guy thinks friction is the force that matter it is not torque is what matters.

But you still think that this torque applies more force to the axle than the plane's engines can.

Prove it.

Lets see if you can follow, one more time for all the people who failed physics.

Let talk about why a plane wheel spins in the first place lets use assume a perfect wheel that never slips and an axle that has no friction.

1. The rotation of the wheel is porportional to the speed of the plane. Do you agree that this is the case. This is a by product of the fact that the wheel never slips. If the plane goes from point A to point B the wheel must have rolled that same distance.

2. 1 works in the other direction the speed of the plane is portional to speed of the wheels because again the wheels don't slip. The wheels roll over the same distance the plane does.

But don't take my word for it just go outside and put your car in neutral and push it. Watch as the wheels move. Now try spinng on of the wheel backwards and watch the car go backwards.

Ok, so now you should understand how a wheel works.

For the plane not to have forward motion all the treadmill has to do is rotate the wheels backwards at a speed greater the plane is rotating them forwards.

You can't possibly be serious. Tell me you're just yanking my chain, or that my sarcasm meter is broken.

Of course you can push a car in neutral. Because the wheels are free spinning, just like an airplane's wheels are. How many times can this be pointed out?

The only torque the freespinning wheels of an airplane apply to the axle comes from rolling resistance between the ground and the tire, and in the bearings, the sum of which is so small compared to the force of a jet engine as to be negligible.