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I think I finally understood the whole plane-on-a-conveyor-belt thing 🤯youtube.com/watch?v=xUjcHW7SHa

· · t2m · 3 · 5 · 7

@tiefpunkt oh wow, I was so prejudiced at the start of the video, but it changed my mind!

@tiefpunkt I'm really curious. The first time you heard about this question, did you think that a plane, that is placed on a conveyor belt matching it's speed in the opposite direction, is able to take off?

@tauli @tiefpunkt I'm surprised that this is so controversial. I find it so obvious that it will take off.

@turion @tiefpunkt I guess that the question whether it's obvious or not has something to do with how many similar problems you have already thought about. Different people find different things obvious or complicated.

@turion @tauli @tiefpunkt
In my experience, people equate "matching its speed in to opposite direction" with "so fast that the plane is held in place".
That is not what would happen to a plane but what _does_ happen to a human or even a car on a conveyor belt/treadmill.

The plane just doesn't use its "feet"/wheels for propulsion, like we do. The wheels on a plane are free spinning so no matter how fast the conveyor goes, it will not keep the plane in place.

@lambdatotoro @turion @tiefpunkt There's a video by Adam Savage that already explains this in great detail. (link in the OP) I'm more interested with the question why people find right answer or not. I had more problems understanding where the confusion comes from than the question itself. But as someone who is interesting in teaching complicated things, I'm eager to know what trips people up with stuff like this.

@lambdatotoro @turion @tauli That was basically the assumption I had made. With that out of the way, it all made sense all the sudden.

@tauli @tiefpunkt i really didn't think of the planes propeller/turbines/whatever and thought 'well, if it has to gain enough speed to take off by accelerating with it's wheels, it obviously never takes off' :D 🤦

@karoshi @tiefpunkt May i ask if you tried to visualize the situation? If not, was it because you didn't think of it, or because you can't? (not everyone can visualize things in their head)

@tauli @tiefpunkt yes, I did :) but in my head I "saw" mainly the wheels and the belt with no clear picture of the plane itself (and weirdly a large hall, like some sort of test station, around that setup :D). Hm, well and then I visualised only the wings and the air around them and that they hat to stay in place, because nothing moved either.

@tauli as Adam Savage says, it's really about the question itself. I always thought that it would not be able to take off, because I never realized that the wheels don't matter, it's all about the air.
My assumption was, that if the conveyor belt were to match the plane's speed, the plane stays in place, based on the assumption that it's about wheels on the ground, not about propellors in the air.

@tauli As soon as I realized that it's not about the wheels, the conveyor belt speed doesn't matter at all, and it's basically impossible for the belt to make the plane stay in place, then it clicked.

@tiefpunkt @tauli
The wrong assumption I had was that the wheel speed is the same as for normal take off, then the plane would stay in place because of the conveyor belt pulling back. But as it moves forward by the propeller, the wheels spin at double speed (moved forward by the propeller + the underground moved backwards), so in total the plane still moves forward as "usual" and can take off.
Very evil question 😉

@tauli ich weiß noch, das ich das erste Mal, als ich davon gehört habe, mir sogar einen jumbojet vorgestellt habe und trotzdem zum Schluss gekommen bin es hebt ab

@MissInformation Mein Problem bei der Frage war, dass ich nicht verstanden hab, wie man überhaupt auf die Idee kommen soll, dass das Flugzeug nicht abheben kann. Hab dann die Frage über-analysiert. Geschwindigkeit ok, aber relativ wozu? Gibt es vielleicht irgendwelche Besonderheiten an Flugzeugrädern, dass die sich ab einer gewissen Drehzahl sperren oder große Reibung entsteht oder so was?

@tauli also savage liegt glaub ich schon ganz richtig, das viele die Funktionsweise des Autos auf das Flugzeug übertragen. Ich glaube zudem, viele wissen gar nicht wie ein Flugzeug tatsächlich funktioniert und deswegen auf Auto zurückfallen.

@MissInformation ja, ich denke das video von Savage trifft den Nagel auf den Kopf

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