Airplane Question that Drove Me NUTS!!!
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- Опубліковано 14 кві 2023
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Imagine an airplane is sitting on a conveyer belt, as wide and long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction… CAN THE PLANE TAKE OFF??
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By: Mehdi Sadaghdar - Наука та технологія
There could be 400 knot headwinds, in which case the plane could take off without needing any thrust at all
The video was released 2 min ago, how tf were u able to comment 8 hrs ago 😂
@@neellohitdash probbly like patreon or channel member early access
Touché!
@@bilalmirza741 look at my comment...
Take off in this situation is probably the wrong word, I would say it would be blown away and crashing somewhere like it would be blown away from a hurricane.
Actually, the real answer is that after a few seconds of thrust, the centifugal forces will cause the plane's wheel to violently explode, letting the entire plane down onto a belt moving at (probably) the speed of sound or higher, causing the plane to be violently shreded and shot backwards. Depending on your definition of plane, you could count some of the debris cutting through the air at 700 miles per hour as "part of the plane flying".
Mission accomplished. We're airborne.
Real answer is that conveyor belt dont exist, because no one is stupid enough to build few kilometers long structure with absolutely absurd requirements.
@@alexturnbackthearmy1907 Really? You must not have been here very long, so let me be the first to welcome you to the planet the dominant inhabitants have named Dirt. Or something like that. As a whole, they're not very bright; despite having demonstrably had the technology for more than a lifetime, they hadn't spread beyond Mud's low orbitals - and barely even that.
Honestly, it's best not to provoke them. Not only are they fairly stupid overall, they tend to irrational violence, and have contrary streak that is nearly immeasurable. That orbital thing? Yeah, one of their leaders basically dared them to do it. Not long after, he was murdered. Not saying the two were related, but not saying it wasn't. Get this though: despite having their leader's braincase publicly and violently ventilated, his people STILL went ahead with the dare!
I always respond to this with "The conveyor belt will explode first."
The technology to construct a conveyor belt which could maintain integrity while holding the weight of a jet airliner WHILE running at the speed required to grenade the wheels doesn't exist, and it is only reasonable to assume that the plane under test is constructed using the same technology as the conveyor.
@@mikehammer4018
This is why I learn English. Things like this motivate me to learn more.
It is vital to understand the difference between airspeed and groundspeed if you actually want to fly.
You would think people that graduated high school would know this. Seems like that's not the case, though.
Yes and when the groundspeed is zero, also the airspeed is and that makes no lift
@@borabengi4583 ground speed has absolutely no effect on air speed. Air speed can be well over 25 - 30 knots (30 miles per hour) while ground speed is zero. Ground speed being zero does not mean there is no lift on the wings of the aircraft. If you're not an aviation enthusiast and dont know about this, dont comment about it
I am more than an aviation enthuisast, i built and flew a lot of RC airplanes and you misunderstood me. İ meant conveyor belt’s speed when i Said ground speed. I know airspeed is independent to ground speed. We both know this one won’t fly without airspeed. Here airplane won’t fly because belt doesn’t let wheels to go faster than it and that means plane will try to move forward from it’s position but it won’t fly because it’s not moving meaning that airspeed will be zero. And without flying off the ground, wheels will blow up due to centerrun effect and crash on it’s belly. So eventually, it will run on the belt but won’t fly and run till wheels get ripped. At least this is what i think.
haha aight, makes sense
The most sensible interpretation that makes it useful to think about IMO is "the treadmill does its best to keep the plane stationary". In which case, the ramp up to infinite speed happens, but not infinitely quickly because the wheels have some angular momentum. And then it becomes more a quality control question of whether the treadmill or the plane wheels explode first. If the treadmill explodes first, it will probably destroy the plane and its engines with shrapnel, and the plane won't be capable of flying after that, but it might get lucky and remain in a good shape to take off from the debris field!
I like how the question is implying that the plane's wheel speed is the sole reason why it takes off.
oh its the wheel? i always thot its the nose.
the wheels will be going twice the normal take off speed, maybe they think the will will explode?😅
i'm pretty sure that part is the whole gimmick behind the question
I mean it kind of is. If the conveyor belt negates the rotation of the wheels there won't be any lift since there isn't any movement
Yeah, that's a fundamentally bogus proposition. Except ... the tires have a rated speed, and if you exceed it by a large enough margin, they'll burst. If your speed relative to the "runway" is twice your rotation speed, you'll probably have one or more burst tires, and that's an industrial-strength Bad Day.
This is like the "I'm 14 and this is deep" equivalent of physics questions
More like "I'm 8 and this is deep"!
Have a little more respect for the average 14 years old :-)
@@SALSN I'm 14 and disagree
@@rcat777 well I did say the AVERAGE 14 years old ;-)
The real question is how TF would you design the conveyor belt.
Xkcd did a response to this that was very thorough and exactly explains why it has this "I'm 14 and this is deep" feeling for a physics question.
4:51 "We can say the value of the belt and the wheel are equal at infinity". As a mathematician, I am disgusted.
This is effectively the same sort of rig used for testing plane landing gears. The plane is effectively 'tethered' in place, with only the wheels turning on the same spot. There is no airflow over the wings. No lift. For regular liftoff the wheels aren't what cause it to take off, the wheels move the plane in order to create airflow over the wing, which is what creates lift. Put simply, if there isn't enough airflow over the wings to lift the plane, it doesn't matter what the wheels are doing.
Exactly and since it doesn't matter what the wheels are doing, the plane will take off REGARDLESS of what speed the belt or wheels are doing (of course if the wheels survive).
@@skatemaster33 it cannot while it is on the ground. The vehicle (car, jet aircraft, rocket, etc.) only moves on the ground by sliding or rolling. If we know that the wheels have to roll in order for the vehicle to move, it is trivial to hypothetically design this conveyor to move 'ground' at exactly the same rate and, by the specific terms given to us, the rate of change is instantaneous so there is no way to out-accelerate the conveyor.
@@MrDefreese that's the thing, the rolling is only because the vehicle moves forward, the vehicle doesn't have to roll in order to move forward. It has wheels purely to you know not to scrape the whole plane across the runway. If the conveyor belt exactly matches the wheel's rotation then the plane has to move since the wheels move because the plane is moving forward. The plane can take off regardless.
@@skatemaster33 it looks like you are not reading the question. the plane moves forward because of the engines (1), hence the wheels turn (2), hence the belt moves backwards the same amount (3), effectively making the plane stationary. The engines alone will not make the plane fly, you need airflow to lift the wings.
@@ricardoolivo5244 yes but the engines are not related tot the wheels in any way. The plane has to move forward because the engine pushes the air not the wheels
you could also consider that the wheels spinning faster and faster causes them to eventually approach the speed of light. In which case the plane would start gaining relativistic mass until it was too heavy to lift off.
Surely they would fly apart long before they reached that speed, but I do wonder what effects rotating at the speed of light would have
@@jdhannan well, since the thought experiment already requires almost infinite energy and frictionless bearings I didn't think indestructible wheels require mentioning
😂
Also the wheels would time travel, and when it stops spinning the plane would have already eroded away :)
reletivistic mass doesnt exist the energy from the momentum would becomse so high the wheel collapses in a black hole. you can explain it with reletivistic mass, but most physisists i know prefer thinking of it as energy from the momentum bending the spacetime.
it is an interesting problem though, because the outside of the wheel would time dilate way more then the inside. you probably need someone studiyng rotating black holes to give a satisfying awnser
1:20 As a pilot I would say "IT DEPENDS", and kinda YES! If you imagine there is also head wind at speed around 160-180 mil/h it would fly easily, even without that belt with wheels totally standing still :D
Most people forget, that only airspeed is important, and ground speed is irrelevant.
EDIT: For people b1ching about: "did you ever saw 150KT wind?"! Its totally imaginary situation, did you ever saw moving belt under 747 at speed up to 300KT?
Which is why they call it flying and not driving.
Have you ever been on the runway (or anywhere) and experienced a 180 mph headwind?
@@chitlitlah not all airplanes are jet airliners. So yeah it’s happened at airports where planes that are not tied down have lifted off the ground in high wind.
I would say NO - there are nothing about headwind or thrust of engines. And as you say - lifting force are created by airspeed, not the wheels speed.
I would say Yes - coz - belt should match the speed of wheels. For wheels to have any speed - thrusters should work. As result 747 would lift in the air and probably would even fly some small distance, but then would drop on the ground due to low initial speed (that's why catapults are used on aircraft carriers, to launch them from small runaway - to give them initial speed).
@@MeppyMan Yeah, I've seen old bombers blow cubs off the taxiway lmao
It doesn't matter if the wheel bearings are frictionless. The wheels can transfer horizontal forces to the plane through the axels regardless of the rotational friction of the bearings. The engines provide some amount of thrust X on the plane. In order to maintain the problem constraint the belt has to provide an equal and opposite force X on the wheels. This introduced a moment on the wheels because the axels are pushing forward with X force at the center of the wheel and the belt is pushing backward with X force at the bottom of the wheel. Make reasonable assumptions for the radius and angular inertia of the wheels and you can solve for the wheels' angular acceleration. The problem constraint can hold (and the plane won't be able to accelerate or take off) as long as the wheels can continue to accelerate at this rate.
The wheels on a plane are free spinning so unless the conveyor belt is able to move so fast that the force of friction of the wheel shaft turning is enough to counteract the thrust of the jets, which almost certainly would destroy the landing gear through the heat produced by the friction, the plane is still going to move forward because it doesn't push against the ground: It pushes against the air and it will have no trouble taking off.
As a flight instructor, this was a pain to explain to my students.
Are people seriously that dumb?
the treadmill could be moving backwards at 10x the speed of the plane, with the wheels spinnig 9x backwards, the plane would still take off, planes takeoff on ice or water literally dragging the ground
@@leandrrob In a real life scenario the plane would stand still until the belt or the wheels will fail. Some people REALLY need to go to school.
@@gmlviper consider the wheels spins independently of the relative speed of the plane/ground. even if the wheels spin at the speed the plane should take off, the turbines still going to push all the weight of the plane and the wheels WILL spin faster but they are not dragging the force of the turbines.
Kinda made me think of a seaplane or something taking off while going up river.
that is exactly the same problem I have with these kinds of questions, they require disregarding some factors to work, but then you can have completely different answers depending on what factors you choose to ignore.
And the premise implies that you should disregard important factors to deceive you. It's just a "gotcha" that makes it seem like a thought-provoking question but it actually isn't.
yep exactly, you would have to assume that the whole conveyor belt is totally unaffected by the laws of physics and perfectly able to match the wheelspeed instantly. So you can either match the ideal conveyor belt to a realistic plane whose bearings would fail at some point or to a ideal plane whose bearings have no internal friction at all and so on.
Also the missing info can cause issues, and adding them changes the question and most times would also change the answer.
We cant assume anythhing. Without forward momentum to force air over the wings, we don't have lift, and no flight.
My final thought, it's not rocket science, but it is the Wright stuff. Peace.
No wind over wings, no take off
I needed this video, I'm an aerospace engineer, I had both professors and colleagues states that the plane wouldn't fly because of the speed matching it got me really mildly mad lol.
On the third solution I actually think it can take off, if friction and thrust match it only means that it won't accelerate, but if the speed is high enough it could take off, also considering that lift is not an on/off thing, but it grows, the friction between the wheels and the conveyor belt is constantly dropping
I don’t know how your professor/colleagues don’t get to the infinite belt speed conclusion.
I’d like to propose a new stupid solution to the stupid question: the belt starts spinning so fast that friction with the air creates enough airflow for the aircraft to lift off with zero ground speed.
They aren't wrong tho
Do they think airplanes are propelled through the air by their wheels? I really worry about these people. Once you realize the trick of the question -- whatever force you apply, only makes the wheels spin -- it's really easy to see through.
@@tsm688 not really, it's more an issue with the interpretation of the Question, considering that is basically a copypasta, you might forget even what was asked and make up the rest, and then you have wrong answers. The Real thing is that it's a stupid thing wrongly wrote
@@riccardobossi5907 the answer remains the same unless you resort to bullshit like light speed treadmills. In any physically possible situation the treadmill is just a red herring.
These questions are an example of memetic ideas. The ones that have proper context and detail die off. The ones that are ambiguous so people keep talking about them persist
Generally made my charlatans like that fw self promoter Derek.
You always know you're going to lose your mind when the question starts with: "Assuming there is air friction"
Bring in the Spherical Cows.
But then we also need to assume that there is gravity.
Without air friction, the wings wouldn't work though, right?
@@jimskywaker4345 Technically speaking, wings work by creating a pressure difference above and below the wing. Air friction is a force that opposes the motion of an object moving through air, thus slowing it down.
Air is mid. World peace can be achieved pretty easily if questions didn't consider air's existence. Change my mind.
Why? Just add a Force in the opposite direction of the direction of movement, done. Unless you're the guy that has to figure out the air resistance of an object.
Absolutely love how you merged in that ad read.. hahaha
LOL, the belt will create additional headwinds and extra ground effect that will significantly reduce the take-off speed. However, as soon as the airplane exits that local wind, it could encounter some issues.
Finally someone else who also knows about ground effect
I've heard this described as a language problem not so much a physics problem. I remember the "Mythbusters" episode years ago, and I got it wrong then, and it pissed me off to no end, trying to figure out where I went wrong. Then my wife explained it to me, and I had it in my mind. For a bit. But I lost it. And now revisiting it has lead me to the conclusion that I am going to plug my ears and hum and live in my world where if air isn't passing over the wings the fricken jet doesn't take off.
You are correct, if air isn't passing over the wing, the jet won't take off.
But the "wheels" of a plane are just bearings. The jet engines push the plane forward on those bearings, so as long as the bearings are free to spin, the plane moves forward.
Yes. The reason why it's a language problem is exactly as stated in explanation 3 of this video. Strictly adhering to the imaginary scenario proposed by the question, the conveyor and wheel speeds reach infinity, invalidating the reality of the scenario entirely so it doesn't fly.
In reality, a conveyor belt does absolutely nothing to an airplane. However, because the impossible physics-breaking infinite conveyor belt is a necessary given in the thought experiment, it makes the plane not fly.
Agreed. These questions are not much better than "Why does 2 + 8 + 9 =10? Because (T)wo, (E)ight and (N)ine spell TEN!" type questions. They are language puzzles
I also got it "wrong". I assumed the engine would be turned off. The question in my mind was, can you cause enough drag winds and ground effect to make the plane take off by just moving the conveyor belt. That was an interesting question. Testing it with the engine on was just so anticlimactic. Of course it takes off if the engine is on!
Randall Munroe (of xkcd fame) wrote a very good blog post about it back in 2008. He sees three possible interpretations:
1: The belt moves at the same speed as the *bottom* of the wheel: the treadmill never moves, because the wheels on a plane taking off are always rolling without slipping. The treadmill acts like a regular runway and the plane takes off. Not many people like this interpretation because it's boring.
2: The belt moves at the same speed as the *axle* of the wheel: the wheels have to spin twice as fast as usual for the plane to take off, which seems doable. This is his favored interpretation, because #1 is boring and #3 has huge problems.
3: Hook up a speedometer to the wheel and have the treadmill move *that* fast: he thinks that this is how most "plane won't take off" people interpret the situation, but he points out that that math only works out if the plane isn't moving, in which case the treadmill also isn't moving and so isn't holding the plane back at all. Once the plane starts moving, the math can only work out if the treadmill speed jumps instantly from 0 to infinite. So in that case the plane can't move because if it were to move the system breaks down immediately and the problem description no longer holds, but obviously a non-moving treadmill can't stop the plane from STARTING to move. Since the description no longer holds once the plane starts moving and doesn't include a mechanism to stop the plane from ever moving, it's...not a great interpretation.
Honestly he deserves some kind of award for the dedication to pull out a treadmill and record his point on it. Bravo Mehdi.
As someone who decided to take physics instead of chemistry in high school i immediately knew the awnser, all the kids in high school called me stupid for it WHOS LAUGHING NOW
Another thing this question made me think was how the rotating belt would cause some air/wind to move backwards due to fluid dynamics.
In general this is not a well formulated question.
I guess you have to make at least one of these videos with no explosions to compensate for that capacitor alarm clock...
But it's still funny as heck.
The video was released 2 min ago, how tf were u able to comment 11 hrs ago 😂
Comment 1h
Video 4 min
@@neellohitdash Patreon early release.
hell
No because the air is not flowing under the wings to generate lift
"I hate it with a mild passion!" 🤣 ... very hard to stay focused with this recurring remark. Super-nicely done!
i love this plug so much😂😂
5:11 i love the vocalised motor noise you made here lol
as someone who grew up watching the Mythbusters it's fun the see that till this day this simple physics problem is still a mystery to a lot of people. Wait till you guys find out about the truck full of birds and the bridge problem.
Mythbusters also got the basic physics wrong on numerous occasions, they're not always a good reference.
If you watched the video you would see that this isn't a simple physics problem. It's actually a failed thought experiment, because it's incomplete in a way that makes it impossible to answer unambiguously. All of Mehdi's proposed solutions are completely consistent with the question and yet, with correct examinations of the physics, result in completely different answers.
@@iffracem So they were like regular physics courses. Neat.
@@iffracem They may have gotten some things wrong from time to time, but that has nothing to do with this particular myth. If the wheels do not have engines attached to them then there is no reason that a conveyor belt will do anything unless the pilot is also applying the breaks. They demonstrated this with an actual airplane and a giant tarp that was pulled by a truck. The plane took off.
As someone who watched the Mythbusters growing up, they messed up a lot. They couldn't even blow up a simple building with natural gas, and yet you see a bunch of news reports about it happening.😮 what other myths did they fail at doing, besides almost killing themselves or others! It's why the show came to an end.
That was a weird one. One of the things I very much dislike about certain tests is multiple choice questions with 2 right answers but the question wants the "best" answer which is subjective. Here's looking at you A+ Cert Exam.
I absolutely hate IT exams. So subjective, and its mostly cramming
the A+ cert can absolutely go fuck itself, I aced it but my god it was absolutely a chore because some of the "right" answers were so patently incorrect (given the information, anyway. I could see how they WOULD be correct if the question was straight up a different situation) that i dont find it surprising that most technicians i work with are fucking braindead idiots
Just say it's not in budget and discussion on the topic will be resumed Q3 next year.
Reminded me of an old soviet anecdote (actually, there are no new soviet anecdotes for some reason):
3 friends graduated from scholl. One went to university to become electrical engineer, one to become school teacher and the last one went to military academy. After their first exam they meet and ask each other about the exam. Future engineer:
- It was easy. Question: "What is the unit for the strength of electric current?" and answers "Volt", "Ampere" and "Watt".
Future teacher:
- Easy indeed. Question: "Is Ampere the unit for the strength of electric current?" and answers "Yes" and "No".
Military cadet:
- Lucky bastards. We've got: "Ampere is the unit for the strength of electric current." and answers "Yes!", "Affirmative!" and "Aye, sir!".
The big trick here is to ignore the rotational system
Best ad transition ever....
The conveyor belt moving would pull air with it, no? If the conveyor belt gets fast enough, this air it's pulling could be enough to let the plane lift off
Hey Mehdi, this got me thinking: can you do an episode on how airplane power outlets work? Like, are they "grounded"? How much draw do they support? Thank you.
Hopefully *_not_* with a practical demonstration triggering the fault switches on purpose, like on those hotel episodes. 😎
An then he pops the plane
Do you want to get on the no fly list….😂 cause that’s how you get on a no fly list. Lol
Probably similar to marine electrical systems which typically are not "grounded" in the traditional sense
@@simond.455 Crew: * hears explosion and swearing in Farsi on plane *
Case 3 is definitely the most realistic, however if the belt is wide enough, the plane will likely take off due to boundary layer and ground effect :)
Might as well factor in the bearings of the conveyor as well...
Except case 3 isn't realistic at all, because the belt motors/bearings would explode as they go to infinity.
Yup, my first thought was "wait what about the boundary layer created by a fast moving belt?"
The non-slip boundary would occur only a few centimeters above the belt. With a high velocity it would make a lot of turbulence. No flow over the wing, and thus no lift. It would probably be sucked down by the pressure decrease due to fast motion of air below the wing. What could theoretically cause flow over the wing would be the air molecules that miss the jet engine intake, but there will be too few of such molecules, so the lift from that would be negligible. So it wouldn't fly.
Boundary layer headwind due to the moving runway surface was my first tought too - question is if the wheels and bearings can handle the rotation speed or not. As for runway (belt) width - apparently it could be of significance if this is a 747-8, as it is classified for a wider minimum runway width than previous 747s, 60 m vs 45 m from what I can tell from some quick googling.
A stationary belt and a runway are identical. The engines provide thrust. The plane flies. The end.
Love this dude.
The question on twitter was phrased poorly I think. The version I know from the past stated that the belt would match the speed of the plane (instead of the wheels). That way it's much less confusing imo.
speed of the plane or speed of the center of the wheel. speed of the wheel is ambiguous (top or bottom of the wheel)?
It wouldn't matter either way, since the wheels are free spinning the plane will move forward regardless of what the ground underneath is doing
@@KaitouKaiju Kond of. Imagine there is a speedometer on the wheel. If the belt is stationary and the airplane starts moving forward at 1 mph, the belt will move backwards at 1 mph. The airplane keeps moving forward at 1 mph, the speedo says 2 mph so the belt speeds up to 2 mph. That makes the speedo read 3 mph, etc, etc. It's an unstable feedback loop that quickly accelerates to infinite speed with the airplane not moving forward at all. Tire structural limits are exceeded, bearing friction melts them down, the airplane stops rolling.
If the riddle is built such that the belt matches a speedometer in the tire, it will not take off because of the wheel's limits. If it is built such that the belt equals the ground speed, it has a chance, but not always.
An A320 tire limit speed is 195 knots, its loft off speed can easily exceed 150 knots. In the second scenario, the tires will be rotating at 300 knots at lift off. They'll likely come apart before rotation.
2 * infinity = infinity
10 * infinity = infinity
infinity * infinity = ?
See where this is going?
@@sirtra introducing aleph one
In the second case; wheels turning on frictionless bearings: the conveyor will start moving backwards at absurd speeds as soon as the plane starts inching forward, but if the conveyor belt is wide enough, there will be a boundary layer of air stuck to the conveyor belt, and the air's viscosity will induce a wind backwards. It's velocity will drop the further away from the belt, but eventually, it will be enough at the wings to induce lift, so the plane will fly without moving forward.
As the plane inches forward, it does so by rolling. The conveyor as stipulated exactly matches that inched forward distance and speed and, mathematically, at the same acceleration rate.
One rotation of a wheel in a unit of time results in pi * wheel diameter in conveyor distance in the same unit of time.
Could you revisit this topic? If the conveyor belt is moving at the same speed as the wheels at all times, the airplane is stationary wrt the ground. Thus no lift can be generated.
The plane will still take off, because you can't keep a plane stationary with just a conveyor belt. Once again, the wheels have nothing to do with its forward momentum, the engines do.
the humor is brilliant! ;'D
Commercial pilot here. 5:27 would be correct - except the tires would explode from overspeed long before you reached that velocity. Even at twice the takeoff velocity, the tires would come apart from centrifugal force.
The video was released 2 min ago, how tf were u able to comment 11 hrs ago 😂
11 hours ago???
@@neellohitdash Bro you have responded to every comment that is a few hours ago, its called times zones, youtube just converts the time they commented into your local time
@@neellohitdash Patreon members get the videos early.
@@jamiemyers4696 no it's Patreon members who get the videos before they are released.
Your content helps me through some tough times that i've been going through while still learning new things.
Thank you, Mehdi!
Same here!
My guess, start of the video: Plane takes off as normal, but wheels spin twice as fast as they normally would. Added drag would just be from the rolling resistance of the tires on the belt and the bearings, which are minimal to the amount of drag an air frame needs to produce lift.
It depends on the airspeed over the wings and the angle. There have been airplanes that have "taken off" due to high winds like a Cessna in a 60 knot winds but it's highly unlikely that the wind would be blowing hard enough in most circumstances to provide enough lift for a 747 (160 knots, almost 200 mph) to takeoff. And the fact that it's on a treadmill with it's engines blast would have zero effect on the takeoff itself, but would obviously matter if you wanted to keep said airplane aloft and not have it crash back into the ground.
The wheels will slide over the conveyor belt and the plane will take off. This is like plane taking off from water. Or if you put sleds on a plane and start it from ice.
However, if you include additional requirement that wheels cannot slide then the only possible solution is that plane stays in place.
This question has even messed with licensed pilots, but I like to look at it in this way:
Stand on a treadmill in roller skates and with the treadmill having a rope tied to the front of it. Hold the rope (important!) and turn on the treadmill full blast. You’ll be stationary, but if you tug even SLIGHTLY on the rope, you will move forward on the treadmill. The forward thrust doesn’t care about the wheels because that’s not the force involved.
But would it be enough thrust for the plane the plane to lift off
@@psgamer-il2pt Yes
The belt is designed to match the wheel speed to forcibly keep the plane in place. Unable to stop the plane, it speeds up until its components cannot take the stress. The conveyor destroys itself and the plane along with it.
You’re halfway to the correct answer! Stand on a treadmill holding a rope. Slowly ramp up the speed of the treadmill. Hold the rope tightly so that you don’t move forward or backward.
Even if the bearings in your rollerskates are frictionless, you’d have to increase the force with which you pull the rope to prevent you from being pushed backwards. That means the treadmill imparts a backwards force through your wheels.
For you to move forward, you’d have to increase your force pulling on the rope, but then the treadmill would match the speed of your wheels increasing the backwards force on your body.
Edit: So you’d never take off!
But when you pull on the rope, the wheels are going faster than the treadmill. In the question it says the treadmill is always matching the wheel speed
This is the definition of overthinking, and I love it.
I Loved This!!
Even in the situation where you have friction everywhere, as the speed of the conveyor belt increases it will be dragging a sizable boundary layer along with it, if the runway conveyor belt is long enough ahead of the plane it would eventually create enough headwind to takeoff from a "standstill" anyway.
Exactly, this is the correct answer. Not sure what this overcomplicated way of saying it won't takeoff is getting at.
Haha, nice solution 😂
Although i wonder, how long is "long enough" for a take-off?
The plane would need enough time to get the engines up to speed while floating.
I would assume that it shortens the runway, but i also wonder how big that 'drop off' moment will be once it clears the artificial wind, kinda like taking off from a carrier.
But that is a lot of friction though.. i imagine the plane rattling and falling apart before the conveyor belt even gets up to speed.
But i guess depending on whatever fins you want to put on the conveyor belt (presumably out of the wheels' trajectory), it could work better, but it would have to go _pretttty_ quickly i think, so it has to be very smooth and durable.
The problem doesn't specify how much air will be dragged by the conveyor belt and whether it will create enough lift, therefore this answer should be discarded as not reliable.
@@Games_and_Music Aircraft engines use either an airstream from a smaller electrically starting turbine to spool up the main engines, or a separate truck with a supersized blower comes by to provide the initial starting flow. Some engines can even electrically start the main turbines by just backdriving the alternators. In any case, the plane's ground speed has nothing to do with engine startup.
Thank you Mehdi! Every time this comes up I say "Yeah, I know the 'correct' answer but the question is silly". In a world with friction there is no way to know whether the plane would take off unless the speed of the belt is defined in a more meaningful way - otherwise it would be a case of testing it and seeing whether the plane could take off with burst tires due to the heat created in the wheel bearings due to ever increasing ramp speed.
Then there's the issue that the draft caused by any belt rotating that rapidly would actually start to generate lift on the wings, lol.
For the friction of the wheel bearing to reach infinity, the friction of the bearings of the conveyor would also need to reach infinity. At which point the conveyor belt would stop and the plane would continue moving forward.
Bearings would be ok for sure, but the rubber is a nother thing.
if the plane isnt moving relative to the earth, (or the wind moving over the wings while the plane is stationary) its not going to take off, period. this has nothing to do with friction or the belt moving at all. Planes fly because of wind over the airfoils. The wheels only turn because of the engine/prop that is "prop"elling the plane using air.
@@yutub561 how about spacecraft, kite or ie. jet ski? Air plane in high altitude? Also in this case "ground" would move relative to plane.
Medhi, I have a similar idea, in this condition the conveyor is rotating in the same direction of the plane’s nose and the constant speed of the plane’s take of speed. And instead of the wheels there are just rods touching the conveyor. The friction is non zero non infinite. The conveyor is as long as it needs to speed up the plane. Will the plane fly? Consider all other conditions that are not mentioned here like earth. I’ll like to watch a entire video about it.
The assumption is that the treadmill belt can move at infinite speed and that the all laws apply to the regular old jet plane, no skidded, sliding, frictionless wheels, no nothing! The wheels being powered or not has zero to do with anything, the result is the same; if the engine pulls the jet forward at 250mph and the airplanes weight on the wheels move the treadmill belt backwards at 250mph, then the plane is going nowhere. The wings only come into play if the plane can move fwd.
2:17 - I usually kill people and run away easily in those dreams.
I think questions like these are intended to get people talking and to get them to realize what assumptions they take for granted. I assumed no bearing friction when I saw the question. So I learned something from the discussion. I think that's at the heart of these kinds of problems
I don't know. I had an exam question like this once, the teacher said you can't assume anything. But I pointed out that you had to assume many things to get the answer they desired (Like, is there gravity). But that question was even missing information needed to calculate the answer. Indeed they even wanted you to assume SATP (not mentioned in the question or exam instructions).
They laughed pittyingly and then said I waa being ridiculous.
@@IRefuseToUseThisStupidFeature yeah I guess it depends on the situation. But I was referring to the one in the video where these are found and debated about on Twitter
The best way to analyse this is to ignore the rotational system. Look at the overall system. If you match wheel speed perfectly at all times that means the plane stays still. To do that you need to apply the same force to the PLANE as the engines do. Forces match the system isnt going anywhere, from 2 physics angles.
You really dont need to drive yourself nuts with the rotational system
No, questions like these are intended to drive social media "engagement."
@@mycosys "If you match wheel speed perfectly at all times that means the plane stays still."
Alarmingly dumb statement. Lock the brakes, coat the tires in grease. Wheel speed zero, runway speed zero. Plane takes off with probably burning wheels.
The wheel speed is not a determining factor of whether the plane flies.
My initial intuition is that the engines push the plane forward not the wheels, so the wheels would blow up because of over speed if the belt always matches them
And I think that we can also add the ground effect caused by the moving air caused by the advance of the belt, a bit like the needle of the hard disk which lifts by rotation of the platers 😄
It would help but not enough to lift the 747 off the ground. If someone tries to do this with a model then it would definitely need to be considered.
@@kamX-rz4uy the plane just have to levitate very slightly above the conveyor for friction to stop taking effect and the jet engine takes over....I wonder if it would reach some stupid contrivance that allows magnus effect to be significant on the wheel as well lmao
there could be a 4th option if you consider te friction between the belt and the air, which can be significant if the belt goes really fast : in this cas it creates a headwind that could provide enough airspeed to lift the plan, although it would be really turbulent
I think the turbulence might not be that big of a deal since the wheels rotate at near infinite speed, acting like the mother of all gyroscopes lol.
At a certain speed, I would imagine the belt would create an air boundary layer and only the air real close to the moving belt would move.
I thought the same
Yes, in this case the Aircraft would pick up Speed about the surface distance of the Belt and then ending up at the Belts end with zero Airspeed. It would need a relative Airspeed twice as high as its stall speed, because when the "belt/air friction generated Air flow" stops, the AC must still travel over stall speed over ground (If Airflow/Wind is zero) to perform a successful takeoff as the question initiates. It could theoretically be lifted, even by a short Belt or even take off if the Belt is long enough.
@@MrT------5743 That boundary layer, if it got fast enough would hit the wheels and create an aircushion the wheels could move forwards on once the sound barrier has been broken and air resistance/speed starts to reduce.
Similarly to how an aquatic airplane experiences a drop of friction with the waters surface per ground speed and gets pushed up once it moves faster than the waves move.
If engineers built planes with wheels that created enough friction to even compare to the force of lift from the powerful engines, no one would be flying today.
Of course, I say this with a mild passion.❤
I wish safe vacuum hyperloops or w/e were real. Damn that would be fast. And if anything went wrong, you wouldn't know.
Think about this.
What makes an airplane fly? Movement of air. Lift. Under the wings.
What is better at making air move, a propeller that is specifically designed to perform this task, or a running conveyor belt with virtually no friction with the air above it? It honestly blows my mind that this debate is still going on.
@@mikegamerguy4776 You mean pneumatic trains? Even if they were safe, no one will ever use one. Because system itself is broken from the beginning.
there's also the fact that the belt isn't just applying torque to the wheels, it's applying a backwards linear force, which gets transmitted through the wheels to the plane body, adding another element to take into account.
Friction is what transmits the backward linear force.
@@TheAdriyaman yeah, friction is how that force is applied, and friction is also why the wheel rotates
That's already mentioned in the video.
@@Sylfa yea my apologies I didnt watch the whole thing first
The rolling resistance of the wheels is negligible. If it wasn't , the wheel bearings and tyres would burst into flame on every take off and landing.
As it is, the brakes sometimes glow red hot when the plane slows on landing
yes. The back force of the conveyor against the forward motion of the plane should not be capable of stopping the plane from taking off. The only caveat is if the wheels and bearings are not capable of handling the load of the plane at the speeds they would need to be turning in this scenario.
I think part of the problem is people seem to think airplanes operate on a time machine built out of a DeLorean principal. The wheels need to reach a certain speed, at which point, the plane takes off. Of course, the wheels on a plane are only there because it causes too much damage to the plane when you let to scrape down the runway. You could replace them with hovercrafts and it would work exactly the same.
The plane isnt moving relative to the atmosphere, so no good amount of air will ever enter the thrusters. The wheels are really only needed to get the aircraft to speed so enough air gets into the thrusters for lift off... that and landing of course. A certain wheel speed is used as a reference point to let the pilots know that once that speed is met, enough air is present in the thrusters to lift off.
@@everstray7482 That is so not true.... The pilots have nothing to do with the speed of the wheels, they dont care about it, heck it's not even displayed on their PFDs. What matters is the speed of the air moving over the wings of the aircraft. When sufficient air moves above the wings of the aircraft, the pilots start rotating (taking off). The speed of the air above the wings might be way above or way below the speed of the wheels, usually a difference of upto 20 - 25 knots. And of course the plane is moving relative to the atmosphere. Please learn the difference between airspeed and groundspeed before commenting your opinion in an open platform like this
@@polytekhat I appreciate the info, but did you really have to end off sounding like a douche? I am all for debate and learning more and seeing where I'm wrong, but people really need to get off their high horses; it isn't about appearing smart, who cares... so stop the pretentiousness.
Look, it's not like i get any sort of satisfaction after being rude to others, nah. The thing is, it took me quite some effort and understanding to grasp aviation, ngl. And when someone, who probably isnt even bothered enough to check their facts, decides to comment their opinion with a high level of confidence, it just really pisses me off. Aviation in a sensitive topic and bad info should be kept at bay at all costs. Its not your comment that brought rage in me, it's the general confidence that non - aviation enthusiasts spread incorrect information with. I've gotten used to it over time and it really is very annoying
@polytekhat Get over yourself or get off the internet because you'll just get pissed off everywhere you look. If you get upset at every little thing, stupid or not, correct or incorrect, you're not gonna have a good time. Besides, text has no tone; if i appeared "confident" in my opinion, that wasn't intended. It was my best guess. It's not like someone's gonna read it, take it to heart, and go be a pilot just like that... 🤦♂️ why a pilot's license is thing my man.... that's the point of a debate like this video, to think and learn from others, not to get upset and shit on others.
I saw that on twitter and my first thought was.. the plane is not driven from the wheels so..... im excited ElectroBOOM is covering this.
It will take off with the wheels not spinning... because the action/reaction produced by the engines is what makes the plan move relatively to air, not the spinning of the wheels (which are a consequence of the movement, not its cause). If the plane had no thrust but motors on the wheels, the plane would have stayed stationary.
I'm impressed at the number of answers you came up with, lol. I wrote this before watching: Only if there's a lot of head wind rofl. That the conveyor belt starts moving at all implies some force is attempting to move the plane forward. We would call that thrust. With headwind in excess of the stall speed and thrust to match the headwind, it could basically hover in place. Whether or not a proper plane can fly is not determined by it's speed. It is determined by the speed of the air over the flight surfaces, the wings. Airspeed determines whether a plane can fly, not wheel speed. And I'm having a hard time believing that even a full thrust 747 is going to cause the magic conveyor belt to move fast enough to push enough air over and under the wings to achieve lift.
Feel like I get an aneurysm every time someone implies a plane's wheels are powered
I thought i was alone…
There are people like me!
Yeah, it's not a car.... 😆
@Tylorean it gets worse once you major in aerospace engineering, I see people who are a thousand times better at math than me not know some really basic stuff from intro classes and I'm just like, why are we spending ten minutes talking about how a v tail works conceptually
@@Th3Shrike The fact you've majored in aerospace engineering yet stopped at "duh the wheels aren't powered" instead of watching the video and seeing all the other ways the plane might be stopped from taking off is giving me an aneurysm
@@Th3Shrike Well just like you don't know some basic stuff in other fields they don't know some basic stuff in your field.
Watching his video-which was released 5years ago- for the first time, made me wonder whether he's still alive. I am so happy that he is. Just subscribed.
What. This was released 3 days ago.
Is there a relative velocity of airflow over the wings? It has nothing to do with the wheels.
I think case 3 is the one that normal people refer to. We need to be assuming negligible winds and all unspecified variables are at realistic values. The wheel bearings have a speed limit dictated by friction but the conveyor belt is all powerful. The moment the plane picks up any ground speed, it’s canceled out by the belt. Thus the plane remains stationary relative to the ground (and therefore the air around it) no matter what.
wheels do not work that way. imagine a car in neutral speeding down a highway. the highway does not stop it.
make the highway a treadmill. The wheels spin faster but so what? A little wheel bearing friction? The car moves anyway.
@@tsm688i made a video proofing, it wont take off.
@@neutronenstern. video != proof
logic = proof
Unless you left the brakes on, the airplane is not coupled to the wheels.
your logic is flawed.
@@tsm688 The wheels do have friction,and this friction encounters thrust. It might be, that the threadmill will habe to go at an insane insane insane amount of speed,but at some point the friction force inside the bearing of the wheel will encounter the thrust of the plane. And due to the question,it will eventually be able to reach this speed, cause else the plane will,asyou said move, and this would imply,that the wheel is turning faster than the belt, which violates the information given in the task. So the plane will not move,and the belt will go crazily fast, and the friction force will encounter the thrust. (notice, that the wheel is indeed attached to the plane, so if it had brakes on,the plane will stop, and of friction is as strong as a brake, then it will also stop,and at some speed the friction will be as good as the best break.
@@neutronenstern. Solutions involving hyperlightspeed treadmills beyond the realms of physics are unacceptable. Getting such a strange result either means
a) the question is gibberish
or
b) you've misinterpreted the question.
Another aspect is: the conveyer has friction with the air above it. as it runs, it moves the air which increases the wing speed and lift.
Ooh ground effect
Yep, but they didn't specify whether that lift will be enough, so we cannot make definite conclusion based on that
@@igorbondarev5226 you're right but there are so many missing details in the question that I don't think it can be answered at all. I just mentioned that this is another aspect to consider.
According to GPT4, because the belt matches the speed of the wheels the ground effect wouldn't come to play because it is dependent on the forward speed of the aircraft relative to the air and the proximity to the ground. The plane remains stationary relative to the surrounding air beneath it's wings. The conveyor belt would create some turbulence and localized airflow close the the ground but it would not create the necessary airflow over and under the wings to generate lift for the aircraft.
@@Globalnet626 That is the thing, frame of reference. Does not matter if I move a volume of air at take-off speed or move the wing at take-off speed.
The easiest way to think about this conceptually is wearing roller-blades on a treadmill, while being tied to a rope attached to a wall in front of you. You can grab onto the rope and pull yourself forward, the wheels on your feet while just rotate more. In the plane's case, replace the rope with air.
Congratulations on being the only person to explain this problem to me in a way i could understand, its been driving me insane, but now i get it, thankyou!
To make your example the same as the question, the treadmill would speed to infinite up as you tried to pull yourself forward, generating so much friction your wheels would melt off.
The only way you could go forward is if you assume some limitation on the belts top speed.
Wheel bearing are low fiction, but not zero. They will cause some amount of drag based on their speed, and with infinite speed you get infinite drag.
@@zncon The belt under that interpretation is unphysical, in that it has to instantaneously accelerate to sufficient speed such that the wheel bearing friction is enough to counteract the thrust.
So we have instantaneous acceleration, which means either infinite force or massless treadmill and treadmill bearings.
@@DevinBaillie Yes, if we try to apply real-world physics to everything this question is just about finding which link of the chain destroys itself first.
@@zncon did you really just assume at the same time that there is friction on the wheels, but not on the treadmill? if you are going to assume the treadmill speeds up infinitely then it is subject to the same problem the wheels have and it will just up and die
A planes motion isn't dependent on it's wheels. It's like a water skier pulling their self toward the boat that's towing them. The boat may be moving at some speed, but the force the skier has to overcome isn't so high that they can't overcome it.
Hello, which textbooks for electrical engineering undergraduates do you recommend every student should own? I am a big fan of your content.
That sound effect at 5:10 🤣
Wheels are only there to be a reasonable bearing so that when the plane takes off (thanks to the engines), there's not too much friction with the ground. It might help to instead imagine the same problem with a seaplane -- a plane with no wheels. There the friction with the ground (water) is prety high, and yet the seaplane can still take off.
but they are desinged for that and have floaters to reduce the friction enought to take off without complications, a normal airplane in the water would get destroyed by the friction before taking off
@@PurpleH4z3 The pontoons don't reduce the friction as much as you'd think. Seaplanes don't have brakes but still stop in reasonable distances.
If there is not too much friction so the plane can move forward it will violate the criterion that the belt speed exactly matches the speed of wheels. The only way for this to happen is when friction is equal to thrust, whatever it takes. I hope less than speed of light is required
I think it does help, but as a demonstration that the wheel doesn't matter.
You can still have all these scenarios Mehdi proposed.
Plane floats downstream until you add thrust. Then you need sufficient thrust to overcome the flow (friction) of water. With fast enough water, you can't stop moving downstream/backward... so turn around lol
I don't think I've seen anyone talk about the plane being pulled backwards so fast that it "weathervanes" and takes off in the other direction lol
what if there is an opposing current that matches the airplane speed? :DDD
Even just sitting there, it is flying... Through space on a hurtling rock😂
The conveyer belt's friction is not enough to stop the plane from flying!!
Jet planes are powered by thrust, not traction. The only possible thing that might prevent the plane from taking off is the possility of the tires bursting from excessive speed. But after V1, that's academic anyway.
Their forward speed is powered by thrust, but air speed over the wings is what gives them lift. Without wings, in a vacuum, or zero air speed over the wings, the plane will never leave the ground.
With frictionless bearings or in the real world, the plane will obviously take off. The problem comes in when you begin to factor the hypothetical conveyer belt that perfectly matches the wheel speed of the wheels. There is friction in the bearings and drag due to that friction. In the real world it takes off. In the hypothetical, where you have indestructible bearings and friction, it doesn't.
@@NG-VQ37VHR It's "airplane on a treadmill" not "airplane in a vacuum".
I'd wager that the treadmill would start creating ground effect beneath the wings and generating even more beneficial lift before you ever threatened to burst the tires from excessive speed.
@@NG-VQ37VHR the hypotetical conveyor belt can go at whatever speed it wants, the wheels are free to rotate and the engines are on the wings and pushing the plane forward
Even when the tires burst, there isn’t enough friction to keep the airplane from accelerating. Maybe if the burst tires damage the aircraft like it did with AF 4590..
electro never ceases to amaze
Conservation of energy. Where exactly are we losing all that thrust from the powerful jet engines if the plane is not taking off?
well in that case depending on the exact conditions of the experiment it is possible if it accellarates the air around it due to friction with the huge conveyor belt. thos could create a liw pressure zone below the plane sucking it down but also accellarating more air in front of the belt so that in theory it might be possible to create sufficient wind speed relative to the plane wings so that it takes off? would have to crunch some numbers for a precise andwer. i think it would be possible depending on wind condition and the exact plane and runway design
Absolutely, it will take off if the tires do not explode. It’s about airspeed vs ground (tire) speed. When the wings feel about 150 knots airspeed over the wing, it will fly. In this situation, the wheels will be turning 300 knots. Remember, the wheels do not drive the airplane forward. The wheels just spin. HOWEVER, the tires on a 747 are rated to about 225 knots and will likely disintegrate before the airspeed is suitable for takeoff. I wrote this before watching your explanation. I think we are close
It is about wing speed vs air speed. If an airplane is going 120mph and a 50 mph tail wind appears the plane will stall and fall out of the sky despite the engines still operating.
The belt is larger, therefore likely to break before the tires do. This will likely destroy the plane.
But it doesnt matter how fast is airplane accelerating and how fast the belt is moving it in the other direction to keep it stationary, does it? Because in the end, even at max thrust, the atmosphere around the plane will be stationary, thus no pressure differential?
But the conveyor belt is stationary so how would there be any wind flowing over the wings, since the plane is at rest with respect to the ground And the conveyor belt?
@@graullas8981 the turbines will suck and push air and create the pressure differential.
I expect that if the belt exactly matches the wheels speed, then all of the engines thrust will be consumed by increasing rotation speed of the plane wheels (they will act like breaks to the thrust force). In reality this would require the wheels to speedup very quickly to insane speed ripping the tires apart, because the rotational inertia of those wheels is very small while the engines thrust is huge.
Continuing on, let's assume that tires and wheels are indestructible, and the belt as well, in that case the belt would increase its speed untill the belt surface reaches almost the speed of light, and so would the tire surface, and at that point i guess that they would slowly increase their speed closer and closer to the speed of light with the rotational inertia of the wheels and tires approaching Infinity, so the finite engine thrust will never be enough to push the plane forward in that scenario so i reckon it can't take off in that situation.
I've seen in the comments someone saying something about belt friction, in that case if the belt has nonzero friction (and it must have nonzero friction to interact with plane wheels), then at sufficient belt speed it would drag enough air with it to create strong wind layers around it dragging more wind layers around those and so on, although I'm not sure if breaking the sound barrier would wreck the effect of layers of moving air sticking to other layers of moving air going at different speed (which is very important for sail aerodynamic efficiency and explains why sails are on purpose not made from super slipper materials).
So in that case perhaps it may be possible, but i think that it would require the belt to reach multiple speed of sound, and dragged air shockwaves may mess up the whole thing, so I'm not sure here.
😳😱😳😱😳
Mass-energy equivalency. If the wheels and belt spin at approximately the speed of light, both become increasingly heavy and the energy concentration could create a black hole. Is the rest of the plane also indestructible?
wheels on aircraft are not powered and all thrust comes from the engines on the wings just pushing it forward regardless of what speed the wheels are turning at. This is car logic that does not work for airplanes
@@marcogenovesi8570
You clearly don't understand the OP's point. Go back to school.
Two things decide how much lift and airfoil can make.
1.) Angle of attack
2.) Airspeed
The oversize conveyor belt unexpectedly tears, jams, stretches, slews off the pulleys, chews up an innocent bird, causes noise complaints from local residents, vibrates excessively until fracture, or otherwise mechanically fails. Resulting debris gets caught in engine intake, and explodes spectacularly.
Yes, because the speed of the wheels have nothing to do with the acceleration of the plane.
I used to watch you when I was younger just remembered you and all the memories flooded back thanks for the hard work with all the videos
@Lonidamine Replying to them only makes it worse. Just silently report it. Calling out "this is a bot" doesn't do anything but add another irrelevant comment.
I think answer 4 is also a case of fishing for reasons that the reflexive "no, it can't" is right.
The question isn't "does the plane take off while sitting still?", the question is "CAN the plane take off?", as in "does it have the capability?". Every plane, before taking off, spends some amount of time at the end of the runway NOT at takeoff thrust. If we interpret the question in the way that makes 4 correct, then NO plane EVER flies, under ANY conditions.
The wheels don't give the plane power, the engines do; so the wheels would spin twice as fast, but the plane would still take off
It's difficult because if the conveyor exactly matches the wheel's speeds the plane can not move.
But yet the jet engine is pushing against the stationary air and not driving the wheels directly, so can move the plane forwards no matter how fast the belt turns (until the rolling resistance of the wheels is so high that it impedes the plane's motion, or perhaps surface air gets moving with the belt).
My though was that the jet engines don't care about the wheels at all.
@@Tankwiper I've found the answer. All of the jet's thrust will go into increasing the rotational inertia of the plane's wheels which while lighter and smaller than the plane still have some mass. If the plane attempts to move forward, the belt will accelerate, creating backwards force via the wheels' inertia. This will prevent the plane from moving unless the belt drags enough air backwards to create lift for a vertical takeoff - assuming an infinitely powerful belt and infinitely strong tyres and wheels.
It's a trick question. Same thing as Derrick did. I'm with you here, hate these kinds of questions passionately. Thanks for going through the possible solutions anyway.
0:40 no because it may require wind force to lift off
my mans walking on a treadmill like a fat man with 5 oscilloscopes behind him lolololololololol
3:09 is the common incorrect depiction of lift.
If the lines return to where they started, no lift is produced. The correct image should have the trailing lines arching downward, which, thanks to equal and opposite forces makes the plane gain lift.
So glad somebody actually acknowledged the problem of the friction of the wheel bearing reaching infinity preventing the plane moving regardless of the fact that wings use lift, the amount of people i've tried to explain that answer to only for them to smugly not get it at all is so painful
Even if the bearings lock the wheels up because of said friction the wheels are gonna slip, or even if the bearings blow out, the arms are gona scratch against the conveyor. Regardles of what happens to the wheels the plane will still move forward.
People don't understand because you are flat wrong. The wheels are irrelevant to the question, as is the moving road surface. There is no point of force between wheel and road surface, The only RELEVANT fact to an airplane taking off is the air speed across the wings.
judging by whats given. Plane starts stationary, can not accelerate past 0 since:
1) wings have no speed relative to air around it since plane started stationary and has no way to accelerate anyway, Up nor forward.
2) as soon as acceleration gained conveyor belt drops its acceleration to 0. hypothetically if delay between these two events is 0 then acceleration RELATIVE TO anything is 0. yes the plane has potential energy but it is stationary.
No wing to air relative spead = no lift.
@@DavidHeich I have a question for you, what pushes the plane forward?
@@coolbionicle jet engines
The problem in this scenario is how the scenario states "the conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction." It FAILS to specify if the speed it's matching is the rate at which the wheel is spinning, or the rate at which the wheel's physical position is changing with respect to the ground that the conveyor belt is sitting on.
In the latter case, it's pretty straightforward; if the wheel's position is changing at a rate of x, the conveyor belt's rate of travel will be -x. In the former case, when the wheel begins to move forward its angular velocity increases with respect to the conveyor belt, so the conveyor belt speeds up to match the wheel, which causes the wheel to spin faster again, and on up until the wheel flies apart due to the feedback loop. Or the wheel starts spinning at the speed of light, in the fantasy land where the wheel is indestructible.
In any case, the wheels aren't what is moving the aircraft forward; they're essentially free-spinning bearings with a non-zero but negligible effect on the aircraft's ability to accelerate. A jet aircraft isn't a car. The engines work by throwing air and combustion gasses backwards, and that is what provides thrust thanks to newton's third law of motion. The only way the conveyor belt will slow down the aircraft enough to prevent it from taking off is if it's spinning so fast that it's able to act on the aircraft through what little force DOES make it through the wheel bearings. Though at that point, the conveyor may also be moving the nearby air fast enough that the wings are able to gain enough lift to take off anyway.
The sound effects of the wheels and conveyor belt speeding up to infinity are the cherry of this video ❤😂
2:22; Unicorns on the plane! 🤣🤣🤣
My guess: You cannot answer the question without knowing how much angular momentum is transferred from the wheels onto their axes as backward momentum. Assuming that the thrust of the plane comes from the engine, and the axes are entirely frictionless the wheels will just spin aimlessly with twice the velocity of the plane in the opposite direction, supplying only upward force, as the plane accelerates as normal, and takes off.
You can easily calculate the transfer of angular momentum by assuming the wheel and axle has the same friction as an automotive wheel and axle setup which can be useful for an order of magnitude calculation.
There could be winds that could help the plane take off. Also putting on full power thrusters can help as well. I don’t know much about planes, but IMO, i think its possible for the plane to take off. I mean, the only problem I see here is that the plane is as long as conveyor belt. Again, just my opinion. Im probably wrong lol. The wheels moving fast might easily disrupt the plane from taking off.
It won't lift off.
Assuming a take off speed of 300kph, the wheels would be moving at 600kph at the point of liftoff. Since the 747 tires are only rated up to 380kph, the tires will explode before reaching liftoff speed, and the plane will crash and burn as its landing gear is destroyed.