Diluted Dante wrote:Yossarian wrote:Just watched the Mythbusters stuff.Spoiler:Spoiler:
GurtTractor wrote:Keep in mind that I never said the plane was being held stationary by anything, that was an assumption most of you lept to.
Diluted Dante wrote:I don't think anyone made this assumptionGurtTractor wrote:Keep in mind that I never said the plane was being held stationary by anything, that was an assumption most of you lept to.
Diluted Dante wrote:.GurtTractor wrote:Keep in mind that I never said the plane was being held stationary by anything, that was an assumption most of you lept to.
I don't think anyone made this assumption
Unlikely wrote:It absolutely would not stay still. They might be free-spinning but they're not frictionless, and they have a sizeable mass pushing them into the ground.
https://blog.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/So, people who go with interpretation #3 notice immediately that the plane cannot move and keep trying to condescendingly explain to the #2 crowd that nothing they say changes the basic facts of the problem. The #2 crowd is busy explaining to the #3 crowd that planes aren’t driven by their wheels. Of course, this being the internet, there’s also a #4 crowd loudly arguing that even if the plane was able to move, it couldn’t have been what hit the Pentagon.
Diluted Dante wrote:I mean I think even this question wording falls under 3. After reading your edit the sencond half contradicts the first.
Yossarian wrote:I’m not sure the question the way it was initially worded in this thread avoided the phrasing trap. To my mind, a “conveyor [...] programmed to move backwards at exactly the same speed as the plane moves forward relative to the ground on the sides of the conveyor” would be moving at a sufficient speed so as to prevent the plane from moving at all, but maybe I’m missing something.
This is the problem! The wording of this quiz is wrong and makes it physically impossible.
Divide this situation to several steps. At first, everything is just the same as in my explanation above. We apply thrust and we run the conveyor belt in the opposite direction. The wheel starts turning. As the plane moves forward – the conveyor belt accelerates. Keep in mind the preassumption “conveyor belt is designed to exactly match the speed of the wheels”.
When the aircraft moves forward then its wheels have to travel further than the conveyor belt has moved back. But this is impossible in this situation. The conveyor belt is designed to match the speed of the wheel – so it will increase the speed. But the plane still moves forward – there is again a difference between the speed of the wheel and the speed of the conveyor belt. But we do not allow such situation! So we increase the speed of the conveyor belt!
Actually, this is not a process that happens in steps – all of this happens simultaneously – the plane tries to accelerate and the conveyor accelerates to keep up with the wheels. Adding to the speed of wheels. And the wheels accelerate even more. So the conveyor belt…
It lasts until wheels and conveyor belt speed reaches infinity. Or until they reach the speed of light. If you wish to know what happens then – consult the screenwriters of Start Treck or Star Wars.
The wording of this quiz is wrong! This case is impossible. It is impossible right from the very beginning where the preassumption is that the speeds will always match. If we know (and we know!) the forces applied on the plane we know that during the takeoff there is a huge imbalance of forces. So quoting the Newtonian law:
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
The object will not stay motionless because we have unbalanced forces. So we can not design the conveyor belt to move at the same speed as wheels.
monkey wrote:I think any slight variation of wording is beside the point. I read it, I thought the point of the question was ‘if a plane is kept stationary, would it take off’. The question is really ‘would this keep the plane stationary?’ but I’d have still read it the first way most of the time, because that just seems like the whole point of bothering with thinking about it in the first place.
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