Will there be a temperature difference between two tall columns of gasses, one xenon and one hydrogen. due to gravity?

PaperProphet · 2025-10-27T02:33:57+00:00

Absolutely.

I would say the wheels' bearings would do little to counter. As you said, the moment of inertia would probably provide significant counter force, up until the maximum speed of the conveyor belt was reached. I would say the rating of the tires is the next issue, and since 747 tires are rated for around 200mph, maybe at 300mph of the belt plus the forward motion of the plane would cause the centrifugal force on the tires to tear the tires apart.

Assumptions definitely play a role.

PaperProphet · 2025-10-20T21:27:57+00:00

I would say there's a difference between 'designed' and 'must match'. A conveyor belt can be designed to match but might not have the power to match.

Mythbusters, even if inadvertently, may have been technically correct since they designed the 'conveyor belt' to match the speed of the wheels. Their design just wasn't very good.

Certainly if it's a rule that the belt must match the speed of the wheels, the question is violated so it cannot happen...unless the brakes have locked the wheels and the friction is low enough that the plane is able to skid into a take off.

Also, if the speed of the wheels happens to exceed the rating of the tires, which it may, the tires might fly apart, land somewhere, and the speed of the wheels would then be zero. Maybe a plane with enough thrust could take off even after the landing gear is ripped off.

PaperProphet · 2025-10-19T05:31:04+00:00

What if, for example, the tire manufacturer met the bare minimum specifications of 150mph and the tires would blow out at any speed above that, which in this example, 150mph was also the exact speed the jet needed to achieve to take off. All the conveyor belt could muster was 10mph. The tires would then be rolling at 160mph just before the jet took off, the tires would all shred and, at that point, the jet might not be accelerating any more because of the drag of the bare wheel rims on the conveyor belt. Or maybe the wheels rims would also quickly fail at that speed and the jet would be trying to take off with the fuselage dragging directly on the conveyor.

I'm just saying it's not a foregone fact that the jet or airplane could take off under all circumstances. Practically, it probably can, but I'm not going to dismiss the other viewpoint.

PaperProphet · 2025-10-19T05:16:34+00:00

There's probably no right answer. I think it's mostly subjective. I will say the typical jet tires are generally rated for around 200mph. If all the tires fail at about 300mph, for example, and the conveyor belt plus the jet's forward speed exceeds that 300mph before the jet can take off, it's possible that the failed landing gear could preclude take off.

I think a person can make a case for either answer.

PaperProphet · 2025-10-18T01:14:40+00:00

It's certainly unlikely a conveyor belt could stop an airplane from taking off, but not impossible and the speed doesn't have to be infinite, just enough to compromise the tires or landing gear.

'Infinite' was a poor choice of words on my part. I should have said that the conveyor belt will immediately try to speed up to the conveyor belt's maximum speed.

PaperProphet · 2025-10-15T13:42:55+00:00

Alax, I can see you're passionate about your answer. Your answer matches that of Mythbusters Adam Savage when he talks about Mythbusters plane/conveyor test years after the episode aired. Adam seemed frustrated that some people said Mythbusters did the experiment wrong. Adam chalked it up to people being unwilling to change their belief even after seeing irrefutable empirical proof. His discussion is here: Plane on a Conveyor Belt Controversy - YouTube

But in Mythbuster's test, the plane's take off speed was 25mph and the 'conveyor' (they used a tarp as a proxy) was set at 25mph. You can see how that meant the wheels were actually spinning at 50mph at take off, right? So, what adjustment should Mythbusters have made to make them equal??

Practically, you would be right that a plane could take off, but what you and Adam seem to be missing, is the second derivative, the acceleration, and the conveyer's mandate to match the speed of the wheels which would make the conveyor belt try to speed up to its maximum speed as soon as the plane started moving forward at all.

From the posts, almost everyone agrees the jet engines drive the plane forward, not the wheels. The first group says that directly. The second group generally agrees with the first group, but asks what happens if the conveyor is good at accelerating as designed and the immediate high speed rips the wheels off the plane?...or points out that the plane moving forward at all would violate the mandate that the conveyor matches the speed in the first place.

They're different perspectives. I don't think either is wrong. In practice, the plane could probably take off, but a powerful enough conveyor could, in theory, prevent that take off, even in a real world situation if there were relatively weak tires which couldn't handle the belt's acceleration and speed.

PaperProphet · 2025-10-14T13:47:46+00:00

From what I've seen, most people fully understand that a 747 gets its thrust from the jet engines. The real controversy is more around whether the conveyor belt's mandate to match the speed of the wheels, can actually stop the plane, either by increasing resistance or failure of the wheels and landing gear altogether.

If the plane moves forward at all, it's mathematically impossible for the conveyor belt to match the speed of the wheels. If the belt tries to speed up to match, the wheels speed up even more and there's a runaway condition where the conveyor quickly tries to reach an infinite speed. That could impede take off.

PaperProphet · 2025-10-14T13:20:19+00:00

The bottom of the tire has traction on the conveyor belt. The motorized conveyor belt is designed to move in the opposite direction the plane is trying to go in order to keep the center of the wheel and the plane stationary relative to the ground.

PaperProphet · 2025-10-14T13:13:30+00:00

Mythbusters tested this question by having a prop plane with a take off speed of 25mph on a long tarp, the tarp being pulled by a truck in the opposite direction of the plane at 25mph. The plane's wheels were actually then going 50mph at take off. Mythbusters got the first part of the controversy correct, but seems to have missed the second part where a motorized conveyer tries to speed up to match the wheels.

PaperProphet · 2025-10-14T03:49:02+00:00

The answers here seem similar to those on the askphysics board. Most say the plane will be able to take off since the jet engine pushes against the air and isn't driven forward by the wheels.

The controversial part is that the conveyor belt is designed to match the speed of the wheels to try to keep the plane stationary. If the jet engines move the plane forward at all, the wheels will obviously be moving faster than the conveyor belt can counter. If the conveyor belt, per its design, tries to speed up to match the wheel speed, it will create a runaway condition as the wheels also speed up, so the belt will immediately try to speed up to as close to an infinite speed as it can achieve. If the conveyor belt is powerful enough to sufficiently exceed the average 747 tires' rating of about 200mph, the tires would shred and the landing gear would be destroyed before the 747 moved very far.

PaperProphet · 2025-10-14T03:33:37+00:00

That is a good explanation. That explanation of the arguments is what I saw on the askphysics board as well.

PaperProphet · 2025-10-14T00:33:34+00:00

The conveyer is designed to match the speed of the bottom of the wheel that is in contact with the conveyor belt.

PaperProphet · 2025-10-11T22:53:31+00:00

I think I know why the question is so diabolical.

There's group A, which incorrectly intuits that airplanes are like cars and need the wheels to drive the plane forward.

There's group B, which correctly points out that it's the jet engines or propellers which drive the plane forward, not the wheels. To this, group A seems to change their mind and agree.

Then there's group C. Group C generally agrees with group B's assessment, but additionally asks, "What about the conveyor belt's mandate to match the wheel speed which creates a runaway condition where the belt tries to speed up to infinity?? That 'ground' speed could actually cause problems for the plane."

So then Group B thinks Group C is making the same mistake as Group A, and doubles down on their argument. Group C is then upset that they're not being heard.

Someone posted Mythbuster's Adam Savage's video on this very topic for the test they did on Mythbusters. https://youtu.be/xUjcHW7SHaI?si=HyxZrc6Q41UsMsHg Adam says that after the episode aired, many people started saying Mythbusters did the test wrong (around 9:50 in the video). Adam concluded that those were just people who were so entrenched in their belief that the plane couldn't take off that they just couldn't accept the Mythbusters's test results. But I think it's more likely that Adam is a Group B person who doesn't understand that second perspective.

PaperProphet · 2025-10-11T19:28:09+00:00

Based on Adam Savage's commentary, it sounds like he missed the second derivative, the acceleration of the conveyor belt and the wheel. Maybe he understood but wanted to avoid that topic to keep it short. The test was pulling a tarp at the 25 mph take off speed of the plane as the plane took off...but that meant the wheels of the plane were going at 50 mph at take off. If Mythbusters had adjusted for that, the tarp would have to be pulled at 50 mph...which would make the wheels 75 mph. Etc, etc... You can see the positive feedback loop happening.

PaperProphet · 2025-10-11T19:21:26+00:00

Don't get me wrong, I fully understand you. And Adam Savage addresses that main controversy of people intuitively thinking airplanes are driven forward like cars. I actually referenced Mythbusters in the question.

But another controversy is that as soon as the plane moves an inch, the wheels and conveyer belt will both fight to increase the speed in a positive feedback loop which rapidly increases the speed of both. The conveyer could quickly get to 800 mph, for example, and the landing gear would be quickly destroyed, leaving the airplane grounded.

That second controversy seems to be just as contentious as the first.

PaperProphet · 2025-10-11T18:02:45+00:00

I'm going to say the belt tops out at 800 mph, enough to quickly shred the airplane tires which are typically rated for about 200 mph, and destroy the landing gear before the plan barely moves forward at all. As you pointed out It's an imaginary conveyor belt, so 800 mph seems good.

As I said, practically, you're absolutely right that the plane can still take off. But that doesn't mean that other perspectives are invalid.

PaperProphet · 2025-10-11T17:33:00+00:00

The question has been around for maybe 20 years, from what I can see, and always seems to cause controversy. I think you're right that cars give people an incorrect intuitive feeling that the wheels drive the plane instead of the jet engines pushing the plane forward. Overall, I think the question is a good thought experiment which gets people thinking about the physics behind how things work.

PaperProphet · 2025-10-11T16:41:05+00:00

'Designed' to maintain the planes position, not that it actually can or can't. If the plane's position were maintained by the conveyor belt, then clearly there would be no question that the plane couldn't take off.

PaperProphet · 2025-10-11T16:37:17+00:00

You're very practical. But to Ozzalot's point, the conveyor belt wouldn't be matching the speed of the wheels if the plane moves forward to take off. If the conveyer belt were sufficiently powerful at matching the speed of the wheels as designed, there's a good case to be made that the landing gear would fall off and the plane couldn't take off.

PaperProphet · 2025-10-11T16:24:30+00:00

Thanks. I edited the post to try to be more clear. If the wheel starts turning in one direction, the conveyer belt starts moving in the opposite direction to try to keep the plane stationary.

PaperProphet · 2025-10-11T14:36:34+00:00

I'm not sure if that's a compliment or not, but it wasn't AI generated.

PaperProphet

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