plane on a conveyor belt?

[eskimo2]

Originally posted by Mini D
PS.. you have to assume the absence of friction. Given that scenario, the belt and the wheel would both instantly go to infinite speed and the fuselage of the plane would start moving.

The belt and wheel would not go to an infinite speed instantly; they would gain rpms by the thousands or millions per second.  By the time the plane ran out of gas, the wheel would have the same energy (stored as rotational energy) as all of the fuel consumed by the plane’s motors.

[APDrone]

Originally posted by eskimo2
I’d like to be the first to apologize to APDrone.  Although he didn’t explain how the conveyor could keep the plane from moving forward, he was right.  If the conveyor prevents the plane from moving forward, it won’t fly.  

If such a system were real, it would literally explode in a second or two.  If it had infinite strength and power and the aircraft wheels and bearings didn’t create heat and also had infinite strength, however, it would work.

Thank you, Eskimo. I gave up trying to explain things. I can see the whole scenario very clearly, but trying to explain it in words has been very difficult, so I quit trying.

<.S>

[Mini D]

Originally posted by eskimo2
The belt and wheel would not go to an infinite speed instantly; they would gain rpms by the thousands or millions per second.  By the time the plane ran out of gas, the wheel would have the same energy (stored as rotational energy) as all of the fuel consumed by the plane’s motors.

You are assuming the absolute absence of friction.

If this were the case, the belt and the wheel would not react at all. The wheel would slide across never turning.

You are eliminating too much to make this scenario possible. Way too much. You are holding onto one constant and completely eliminating several others.

There really is one correct answer: The scenario described is impossible. Come up with a real question.

[eskimo2]

Originally posted by APDrone
Thank you, Eskimo. I gave up trying to explain things. I can see the whole scenario very clearly, but trying to explain it in words has been very difficult, so I quit trying.

<.S>

Unfortunately, I think that only you, I and hitech get it.

The problem is the question was worded poorly and appeared to be based on a major misunderstanding: that planes wheels have anything to do with propelling them forward.

[Mini D]

You're still missing most of the basics eskimo. You don't really understand anything.

you cannot rotate an object without friction. Period.

If you have friction, then you are running into the following scenario which has been stated over and over: The belt would have to be capable of spinning the wheel so fast it would destroy it.

Anything more abstract is impossible because you're inserting 0 as a divisor somewhere.

[eskimo2]

Originally posted by Mini D
You are assuming the absolute absence of friction.

If this were the case, the belt and the wheel would not react at all. The wheel would slide across never turning.

You are eliminating too much to make this scenario possible. Way too much. You are holding onto one constant and completely eliminating several others.

There really is one correct answer: The scenario described is impossible. Come up with a real question.

No, friction between the tire and conveyor is essential.  But it’s not wheel friction that’s holding the plane back.  The conveyor is delivering its energy into the aircraft’s wheels’ in the form of rotational energy.

The only impossibilities of this system are that it has absolute strength and power as does the wheel and bearing (also immune from heat).

It clearly is impossible in real life.  Theoretically with absolute strength and power, however, it would work.

[Mini D]

How do you spin the tire? There can be no friction between the axle and the wheel. In this scenario, energy cannot be transfered to the wheel.

That is absolute.

[lukster]

IT'S A TRAP!!!

[eskimo2]

Read this again:

Imagine that we are only talking about an aircraft wheel with say a mass of 100 lbs and no aircraft, sitting on a treadmill. Turn the treadmill on at 10 mph suddenly and the wheel will start rolling back. It will drift back until its rpm gets up to 10 mph. If you were holding a rope, tied to a mass-less axle through this wheel, however, you could hold it in place. You would feel a tug at first, then once it was up to 10 mph you would feel almost nothing and could hold it in place with one finger.

Now imagine that at the end of 1 second the treadmill is going 10 mph, at the end of 2 seconds it is up to 20 and so on. In this situation you would feel a constant pull. This force would be insignificant to a big aircraft engine, but to you, you would definitely feel it. Now exaggerate the snot out of this rpm example; if the wheel and treadmill can be accelerated up to infinity very quickly and still hold together (and not burn up) we could be talking about big forces. If this treadmill and wheel accelerated up to 1,000,000 rpm in 1 second, the rope would tear your arm off.

[JB88]

[eskimo2]

Once again;

Originally posted by hitech
I agree on the moment argument. You could theoretically  create a large enough force to hold the plane.

HiTech

[Mini D]

OOO! HiTech agrees!

There are two possible scenarios:

1) You destroy the wheel because in order to turn it, you need some type of friction between the axle and the wheel and the "conveyer" and the wheel. The heat generated would be as infinite as the rotation possiblities and destroy it.

2) You don't have any friction and the wheel doesn't spin at all while the plane scoots down the runway.

To get anything else, you have to ignore way too much. It is not possible to affect the inertia of the wheel without friction.

[eskimo2]

I’ve stated repeatedly:
It would require unlimited strength for the conveyor, wheel and bearing.  
The conveyor would also need unlimited power.  
The bearing would have to be immune to heat.  
The tire would obviously require friction/traction on the conveyor.

In real life it would explode in a second or two; there is no question that this is theoretical only.  

The wheel bearing could have typical bearing friction, but it is immune to heat.  Or, it could be “frictionless”.  Yes, there is no such thing but physics books refer to them often for theoretical or simplified problems.  Friction and pressure are not the same.

[Mini D]

Originally posted by eskimo2
I’ve stated repeatedly:
It would require unlimited strength for the conveyor, wheel and bearing.

Now, you're making things up.

The conveyor would also need unlimited power.

Now, you're making more things up.

The bearing would have to be immune to heat.

If it is turning, there is friction and it is impossible to be immune to heat.

The tire would obviously require friction/traction on the conveyor.

Once again... if there is friction, there is heat. There is no other solution.

In real life it would explode in a second or two; there is no question that this is theoretical only.

It is not theoretical, it is situational. A situation where you have eliminated the impacts that don't support your outcome in order to generate the desired effect.

There cannot be infinite motion in the presence of friction. This is a fundamental impossibility. You cannot move the wheel without friction. This is also a fundamental impossibility. With neither of these being possible, it is impossible for the inertial situation you described to occur. This is not a fixed axle, it is a bearing system. The wheel is not being driven, it is simply an insulator between the aircraft and the ground. If you remove friction (or heat), it is the ultimate insulator.

[eskimo2]

MiniD,

You took high school and/or college physics?  Right?
Don’t you remember solving theoretical problems with frictionless surfaces, pulleys and wheels?

I remember the problem below from my high school quarter 1 physics final:  (It stuck with me because it was so easy.)



Later on we had to solve the exact same kinds of problems only with a coefficient of friction for the table and sliding object, but the pulley and string were still frictionless.  

It doesn’t matter if the string and pulley must have friction for the pulley to spin.  It doesn’t matter that the pulley’s bearing couldn’t really be frictionless.  All that matters is that the pulley is so good that the friction is so negligible that it doesn’t matter.  This does not mean that all friction in the universe must be turned off; other parts may, or may not have friction.  High school and college courses and text books accept the concept of frictionless pulleys, wheels and surfaces for the sake of theoretical/negligible problems.

The airplane’s wheel bearing is so good that it is essentially frictionless; that’s what the design of a bearing strives for.  The tire and conveyor still have enough friction to keep the wheel from skidding.  Now get over that point and look at the problem.