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[FWNuke]

Even if the bearing have zero resistance, the tires still do. Since the tire resists the treadmill, the plane will still move backwards if not anchored or propelled by the prop.

The treadmill grabs the tires and the tire resists. The plane is attached to the tires. I guess I should say tyres.

You kind of made my point about the resistance not changing at steady speeds, which is true. By the faster the treadmill goes, the more rolling resistance you have. Take it to crazy numbers and maybe we reach a point where the plane doesn't take off.

I still think you are stuck on the bearings though.

 

[Krazeh]

Even if the bearing have zero resistance, the tires still do. Since the tire resists the treadmill, the plane will still move backwards if not anchored or propelled by the prop.

The treadmill grabs the tires and the tire resists. The plane is attached to the tires. I guess I should say tyres.

You kind of made my point about the resistance not changing at steady speeds, which is true. By the faster the treadmill goes, the more rolling resistance you have. Take it to crazy numbers and maybe we reach a point where the plane doesn't take off.

I still think you are stuck on the bearings though.

What transfer the force from the wheels to the plane? How is the energy involved in the rolling movement of the wheel transferred to the rest of the plane? What part of the plane is responsible for that energy transfer?

 

[FWNuke]

Think of it another way. Just put a tire by itself on the treadmill and turn it on. The tire will move backwards. It will roll a little, but it will still move backwards.

There is no bearing to confuse.

 

[FWNuke]

What transfer the force from the wheels to the plane? How is the energy involved in the rolling movement of the wheel transferred to the rest of the plane? What part of the plane is responsible for that energy transfer?

The plane is attached to the tire. How can the energy not be transferred to the plane? I just threw out the imaginary zero resistance bearing, but it's still physically there....it just has no resistance to rotation. The lateral force coming from the rolling resistance is applied to the plane.

 

[Son of Sluggish]

All the scenarios you have proposed for why the wheels would prevent an airplane taking off have required the wheels to be attached to a drivetrain.

Yes, this is twice you've accused me of this. Please show me where I said any such thing.

 

[Krazeh]

The plane is attached to the tire. How can the energy not be transferred to the plane? I just threw out the imaginary zero resistance bearing, but it's still physically there....it just has no resistance to rotation. The lateral force coming from the rolling resistance is applied to the plane.

How? If the only thing attaching the wheel to the plane is the wheel bearing, which it is, then any force must be transferred through that. If the bearing is frictionless then the backwards movement of the ground will cause the wheel to rotate and that's it, none of the force acting on the wheel will be transferred to the plane itself and it will sit completely still. You can't look at it in the same way as a tyre in isolation as when you do that you are no longer considering the weight of the plane which will make it want to stay at rest.

 

[Krazeh]

Yes, this is twice you've accused me of this. Please show me where I said any such thing.

All of the following would require the wheels to be driven by the plane for their actions to have any impact on the planes forward motion.

The most basic principals of Newton's law are at work here: Objects (mass) at rest stay at rest, objects (mass) in motion stay in motion. It requires ENERGY to change each of those from one to the other. It is possible (and required by the rules of the experiment) for the energy of the conveyor belt exerting itself against the wheel of the plane (in the form of rotational inertia) to sufficiently cancel out the forward thrust of the propeller.

So... The planes wheels spinning is just incidental... The extra energy required to get get them spinning (illustrated in their continued spinning after the plane leaves the ground) had no affect on the plane's takeoff distance...

The heavier (more massive) the wheels, the greater the rotational inertia and the easier it will be for the conveyor belt to prevent the plane from moving forward.

You're almost on to it! The conveyor belt is matching he wheel speed. That means long as the plane attempts to move, the conveyor belt will be accelerating the wheel speed.

 

[FWNuke]

How? If the only thing attaching the wheel to the plane is the wheel bearing, which it is, then any force must be transferred through that. If the bearing is frictionless then the backwards movement of the ground will cause the wheel to rotate and that's it, none of the force acting on the wheel will be transferred to the plane itself and it will sit completely still. You can't look at it in the same way as a tyre in isolation as when you do that you are no longer considering the weight of the plane which will make it want to stay at rest.

It's the same thing as just a tire by itself.

Are you saying that just because the bearings have no resistance to rotation, that that negates the rolling friction to the plane? Honestly, I don't think you are understanding this.

To give you a different perspective, picture the treadmill starting really, really slowly. The weight of the plane increases the friction to the tire (as opposed to just a tire by itself) and if you start the treadmill slowly enough, you could move the plane without rotating the tire at all, regardless of magic bearings or not.

 

[Krazeh]

It's the same thing as just a tire by itself.

No it's not.

Are you saying that just because the bearings have no resistance to rotation, that that negates the rolling friction to the plane? Honestly, I don't think you are understanding this.

I'm saying that because the bearings have no resistance to rotation that negates the rolling friction of the wheel on the axle. Without that no force can be transferred between the wheel and the plane and they are 2 unconnected systems.

To give you a different perspective, picture the treadmill starting really, really slowly. The weight of the plane increases the friction to the tire (as opposed to just a tire by itself) and if you start the treadmill slowly enough, you could move the plane without rotating the tire at all, regardless of magic bearings or not.

The friction between the tyre and the ground doesn't matter, it's the friction at the point the wheel (and therefore the tyre) connects to the plane, i.e. the wheel bearings, that is important. To get the plane moving you need to apply energy, if the point between the wheels and the plane is frictionless energy cannot be transferred from the wheels to the axle so the plane will not move. The plane moves backwards in normal circumstances because the inherent friction in the wheel bearings locks the wheel to the axle and therefore the plane, and the backwards lateral movement of the treadmill is applied to the plane as a single object. However once you apply sufficient energy to overcome the friction in the bearings the wheels and the plane again become two separate systems and for all intents what each of them does has no impact on the other.

To put it another way, in order for the wheels to move the plane backwards they would have to apply a lateral force to the axles of the plane, they can only do this if there is something connecting the wheels to the plane, i.e. the friction in the wheel bearings causing the wheels to be locked to the axle. If there is no friction then there's no way the wheels can apply a lateral force, they will simply spin.

 

[FWNuke]

The bearings ARE there and they ARE attached to the plane. They are physically able to support the plane and they are able to function in every way as a bearing.

Just because we are giving them ONE attribute of no friction does not mean they don't perform all the physical requirements of a bearing on an axle. The plane is physically attached to the wheels through the bearings. Their lack of resistance to rotation has nothing to do with any of this.

Same as a tire by itself. No different.

 

[Krazeh]

The bearings ARE there and they ARE attached to the plane. They are physically able to support the plane and they are able to function in every way as a bearing.

Just because we are giving them ONE attribute of no friction does not mean they don't perform all the physical requirements of a bearing on an axle. The plane is physically attached to the wheels through the bearings. Their lack of resistance to rotation has nothing to do with any of this.

Same as a tire by itself. No different.

To be honest I hope i'm being trolled because if you really can't understand why the friction in a wheel bearing has a huge impact on any tranfer of force from a free-spinning wheel to it's axle then I seriously do worry about the american education system.

Gonna ask again tho, what is it that you think allows any force acting on the wheels to be transferred to the plane itself? Which part of their physical connection allows that transfer and why? What is the point of bearings if it is not to reduce friction between two items, i.e. allow them to act as closely as possible as independent systems?

 

[FWNuke]

To be honest I hope i'm being trolled because if you really can't understand why the friction in a wheel bearing has a huge impact on any tranfer of force from a free-spinning wheel to it's axle then I seriously do worry about the american education system.

Gonna ask again tho, what is it that you think allows any force acting on the wheels to be transferred to the plane itself? Which part of their physical connection allows that transfer and why? What is the point of bearings if it is not to reduce friction between two items, i.e. allow them to act as closely as possible as independent systems?

You are the one who does not get this. You do not understand that I am talking about rolling friction....the tires surface meeting the treadmill surface. That creates a lateral force, not a rotational force, on the tire. The Tire is attached to the plane. The bearing has nothing to do with the transfer of lateral force to the plane. The bearing resists lateral force. I'll say it again. The bearing resists LATERAL force.
It's no different that a tire by itself. You are wrong. A tire by itself is the most basic example of rolling resistance. According to you, the tire should just stay in one place if the treadmill moves. That's not the case.

 

[FWNuke]

If I grabbed the tires so they wont turn.....and I mean grabbed them so that I am balancing them, not restricting their rotation.....just grabbing the tire at 3 and 9 oclock and holding it like that.. and slide the plane backwards, do you think it matters if the bearing have zero resistance to rotation? You think the plane wont move?

Well, that's essentially what you are saying.

 

[Krazeh]

You are the one who does not get this. You do not understand that I am talking about rolling friction....the tires surface meeting the treadmill surface.

No, I get that.

That creates a lateral force, not a rotational force, on the tire. The Tire is attached to the plane. The bearing has nothing to do with the transfer of lateral force to the plane. The bearing resists lateral force. I'll say it again. The bearing resists LATERAL force.

When you apply a lateral force to a wheel on an axle what does it want to do? That's right, rotate around said axle, i.e. the lateral force becomes a rotational movement of the wheel about it's fixed point. Can we agree on that?

Now, assuming that we can agree on the previous point what happens when the treadmill applies a lateral force to a wheel on the plane? The wheel wants to rotate but is prevented from doing so by the friction in the wheel bearing and is essentially locked to the axle. At this point the lateral force acting on the tyre is transferred to the axle as a lateral force and then onto the undercarriage strut and the plane itself, again as a lateral force. Ergo, the plane moves backwards.

If we now look at the same scenario but with a frictionless bearing there is nothing to prevent the wheel rotating around it's axle. Therefore when we apply a lateral force to the tyre with the treadmill the wheel is free to rotate and the lateral force you have applied simply becomes a rotational movement of the wheel. No energy or force is transferred to the axle or onwards to the rest of the plane and the plane remains at rest while the wheel spins at the same speed as the treadmill below it.

It's no different that a tire by itself.

It's completely different.

You are wrong.

No, i'm not.

A tire by itself is the most basic example of rolling resistance. According to you, the tire should just stay in one place if the treadmill moves. That's not the case.

No, that's not according to me at all. I fully accept that if you place a tyre by itself on a treadmill by itself it will move backwards. But then you've removed the axle and the fact the tyres on a plane are connected via bearings to a object that is much greater in mass than they are.

 

[Krazeh]

If I grabbed the tires so they wont turn.....and I mean grabbed them so that I am balancing them, not restricting their rotation.....just grabbing the tire at 3 and 9 oclock and holding it like that.. and slide the plane backwards, do you think it matters if the bearing have zero resistance to rotation? You think the plane wont move?

Well, that's essentially what you are saying.

If you lock the tyres in place then of course the plane will move back as the treadmill moves back. In such a scenario the tyre, wheels, wheel bearing, axle and plane are all acting as one system and any force you apply to the tyre will act on the entire system. However the only thing normally causing the wheels to be locked in place are the brakes, or the inherent friction in the wheel bearings. If the wheels aren't locked in place, i.e. are free to rotate, then the tyres and wheels are one system, and the axles and wheel bearings are another system. They are unconnected and you can't transfer a force from one of them to the other.

 

[FWNuke]

I think that you think you get it, but you still don't.

Nothing is resisting the rotational motion of the tire at the bearing, which it true. However, the tire is resisting the treadmill and that creates a lateral force on the bearing too. The bearing does resist the lateral force.

Lets say the plane weighs 50 tons and the tires are 6 inches in diameter. (just so you might grasp what I am saying)

You could start the treadmill so slowly that the tires would not rotate at all and the plane would move. The resistance of the tires to the treadmill is transferred laterally through the bearing.

Same thing with a tire by itself. You could move the treadmill at a such a slow speed that it would not turn either.

If you take this to an extreme, you could increase the rolling resistance to the point that the tire is glued to the treadmill. Move the treadmill and the lateral force is still transferred through the bearings. Just because the friction is nowhere near that point doesn't change the fact that the lateral force is still transferred through the bearing.

 

[Son of Sluggish]

I've really got to apologize fellows... The way you come off with the putdowns and smarmy attitude, I took you all for a lot smarter than you really are. First of all, let me say that I have been an avid buff of aviation my whole life and have no misconceptions whatsoever on how aircraft propulsion works. I am quite aware that an airplane's jet or prop pushes or pulls it through the air and the wheels are just there to disengage it from the friction of the earth (unless the brakes are applied). HOWEVER...


This is a good way for you all to test strength between yourselves and your buddies. Secure a wheel to a fixture and with one motion see how long you can get it to spin. Just grab hold of that fucker and spin it with all of your might. You try as hard as you can and you can only get it to spin for 45 seconds. Now, your burly badass boyfriend... He spins it and gets it to spin for 90 seconds. What does this say about how much energy each of you put into spinning the wheel? It means your badass burly boyfriend put exactly twice the energy into spinning the wheel.


WHAT THE HELL DOES ANY OF THIS HAVE TO DO WITH AN AIRPLANE ON A CONVEYOR BELT???


I'm glad you asked.


First of all, don't get mad at your boyfriend for being stronger than you; that's what attracted you to him in the first place. Second of all, don't get mad at the wheel because it is just following Newton's basic law which is that an object at rest tends to stay at rest. Spinning a wheel to see how long it spins... Throwing a ball to see who can throw it the furthest... It's all basically the same thing: Exert enough energy to move a lazy object. This phenomenon can be expounded to say that a moving object doesn't like to change speeds also. Think of yourself in an automobile and the feeling of being pushed back in the seat when you push the accelerator down or being thrown forward when the brakes are applied. In this example (among others) you are the lazy object.


Back to the wheel...


Let's try the same thing with different wheels. Wheels of the same diameter but different weight (mass). The first wheel that you and your boyfriend spun weighed 5 pounds. This next one weighs 10 pounds. What do you suppose will be the difference in your spinning outcome? Before you answer... Let's throw another unit of measurement in: Speed. With the first wheel, you were able to get the wheel going 30 miles per hour and your boyfriend was able to get it going 60 miles per hour. That second wheel is twice as heavy (massive) and takes a lot more effort to get it moving! On the second wheel, the one that has twice the mass, you were only able to get it moving 15 miles per hour and your boyfriend was only able to get it going 30 miles per hour. By the information given can you tell HOW LONG each spin will last? HOLD ON THIS IS WHERE IT GETS TRICKY!! Since the wheel with twice the mass takes twice the energy to move to a specified speed, it will also retain said energy for twice as long therefore... your wimpy 15 mile per hour spin will last... 45 seconds!! And your boyfriend's... 90 seconds!!!


An airplane's wheel will continue to spin after it leaves the ground. Exactly as described above, the amount of time it continues to spin is directly related to the amount of energy was exerted upon it to accelerate it to its highest speed. The greater the mass, the greater the energy expelled and the longer it will spin. Convexly, the less mass the less energy and shorter the time it will spin. To the point where, if the wheel has zero mass, it will have zero energy applied to it, and will stop spinning the second it leaves the runway.


Where does the wheel get this energy? Why it saps it from the forward momentum of the airplane. Even though the engine (as we all know) isn't connected to the wheels (LOL) they are still connected and directly related to one another. In fact, if you could introduce enough rotational inertia into the equation, say with a conveyor belt accelerating fast enough in the opposite direction, you could, dare I say, prevent the plane from taking off...

 

[Scouse]

Hey SoS. Can you leave Krazeh and FWNuke to argue the toss. You've already lost the "plane doesn't take off" argument

 

[Son of Sluggish]

Hey Nuke! The skinny tie is a good look for you! I miss the skinny tie...

 

[Son of Sluggish]

Hey SoS. Can you leave Krazeh and FWNuke to argue the toss. You've already lost the "plane doesn't take off" argument

Hey Scouse. The fact that you can't grasp basic physics doesn't make me the loser.

 

[FWNuke]

Put another way. The bearing is part of the tire and the tire wants to move laterally, and does.

Put a tire with the magic bearing on the treadmill and the tire will move but the bearing wont rotate because it offers zero resistance. The bearing DOES move laterally with the tire though.

Put it another way.

Put a perfectly balanced unicycle with the magic bearing on the treadmill. When you start the treadmill, the unicycle will fall over and the tire will move backwards.

 

[FWNuke]

Hey Nuke! The skinny tie is a good look for you! I miss the skinny tie...

Gotta love the eighties, lol.

 

[Krazeh]

I think that you think you get it, but you still don't.

Nothing is resisting the rotational motion of the tire at the bearing, which it true. However, the tire is resisting the treadmill and that creates a lateral force on the bearing too. The bearing does resist the lateral force.

Lets say the plane weighs 50 tons and the tires are 6 inches in diameter. (just so you might grasp what I am saying)

You could start the treadmill so slowly that the tires would not rotate at all and the plane would move. The resistance of the tires to the treadmill is transferred laterally through the bearing.

Same thing with a tire by itself. You could move the treadmill at a such a slow speed that it would not turn either.

So you honestly believe that applying a lateral force to the wheels of a 50 ton aircraft, with frictionless wheel bearings, would end up with all the force being transmitted laterally through the bearing and onto the axle before it causes the wheel to start spinning? Because obviously the force to move a 50 ton aircraft is far less than that required to start a wheel spinning on a frictionless bearing.

If you take this to an extreme, you could increase the rolling resistance to the point that the tire is glued to the treadmill. Move the treadmill and the lateral force is still transferred through the bearings. Just because the friction is nowhere near that point doesn't change the fact that the lateral force is still transferred through the bearing.

If the tyre was glued to the treadmill then it'd no longer be rotating and would for all intents be locked to the axle, at which point the friction in the wheel bearing is meaningless.

Put another way. The bearing is part of the tire and the tire wants to move laterally, and does.

Why does it? I'm fairly certain most tyres i've seen connected to an axle which is in turn connected to an object larger than the tyre want to rotate when you apply a lateral force to their outer surface

Put a tire with the magic bearing on the treadmill and the tire will move but the bearing wont rotate because it offers zero resistance. The bearing DOES move laterally with the tire though.

Assuming the tyre isn't connected to an axle or object with a greater mass then yes the tyre and the bearing will both move laterally backwards on the treadmill.

Put it another way.

Put a perfectly balanced unicycle with the magic bearing on the treadmill. When you start the treadmill, the unicycle will fall over and the tire will move backwards.

As long as the perfectly balanced unicycle had a greater mass than the tyre it'd do no such thing. If it could remain upright at rest then it'd remain upright when you started the treadmill.

 

[Krazeh]

Where does the wheel get this energy? Why it saps it from the forward momentum of the airplane.

Via what mechanism?

Even though the engine (as we all know) isn't connected to the wheels (LOL) they are still connected and directly related to one another. In fact, if you could introduce enough rotational inertia into the equation, say with a conveyor belt accelerating fast enough in the opposite direction, you could, dare I say, prevent the plane from taking off...

Not sure what's so funny about the wheels not being connected to the engine but i'd love to know how you think they're connected in any meaningful way. And to get to the point where the actual spinning of the wheels stopped the plane from taking off you'd have to have gone well past the point where the entire undercarriage had heated to the point of destruction.

 

[FWNuke]

Why would the mass of the unicycle matter? I thought you said no lateral force could be transmitted through the bearing.

 

[FWNuke]

Also, the 50 ton aircraft with the 6 inch wheels. The wheels would essentially be glued down to the treadmill by FRICTION.

 

[Scouse]

Y'see Krazeh. I told you to leave 'em to it

 

[Krazeh]

Why would the mass of the unicycle matter? I thought you said no lateral force could be transmitted through the bearing.

I never said any such thing, I've never disputed that there are times when a lateral force couldn be transmitted through a bearing.

Also, the 50 ton aircraft with the 6 inch wheels. The wheels would essentially be glued down to the treadmill by FRICTION.

At which point we're no longer discussing a plane with free-spinning wheels are we? If the wheels are glued to the treadmill they're not free to spin and are essentially locked to the axle, as such any force acting on them will be transmitted to the axle and the rest of the plane.

 

[Son of Sluggish]

Not sure what's so funny about the wheels not being connected to the engine but i'd love to know how you think they're connected in any meaningful way. And to get to the point where the actual spinning of the wheels stopped the plane from taking off you'd have to have gone well past the point where the entire undercarriage had heated to the point of destruction.

It's funny because that one northerner accused me of implying that an airplane gets its thrust from its wheel. Only a scouser would think something as ridiculous as that.

Via what mechanism?

Why... You don't think that an airplane is physically attached to its wheel? If there is inertial force pulling back on the wheels, it is pulling back on the entire plane.

In fact... If you take a small plane like a Piper Cub... Next to the engine, the wheels probably hold the most mass of any component in whole plane. With its weak thrust to weight ratio, it wouldn't take a whole lot of rotational inertia to prevent it from moving forward. Of course, if the conveyor belt reached its maximum speed, rotational inertial would cease and the plane would move forward.

I don't expect any of you to understand this.

 

[Krazeh]

Y'see Krazeh. I told you to leave 'em to it

Yeah but I wanna see if it is possible to educate a Yank. So far it'd appear not. They seem to live in a strange world where if you spin a wheel it doesn't spin, it instead tries to move the entire object it's connected to backwards.