I thought redefined and brando were on crack when I first read their response. But then brando's example of an airport walkway got something to click. And wildsweet&cool's post totally cleared up for me. I understand now and am in agreement that it should fly.
it will take off. a conveyor belt is not going to stop a plane from taking off anymore than the spinning of the Earth is. The Earth spins at something like 1000mph, no? I'm sure there are many runways aimed exactly in opposite direction to the spinning of the Earth. So essentially, the Earth is a conveyor belt going at 1000 mph. It hasn't stopped a plane, yet.
See, this is why it's such a poorly-worded 'riddle'. Those people who say 'it will take off, the wheels will just turn twice as fast' or some variation thereof simply don't understand the essence of the riddle. Neither does the 'straight dope' guy, nothing against him. Gravity IS a force. In fact, in flight, it is the primary force to reckon with. Therefore, a plane sitting still must overcome ALL of its standing-still inertia in order to start moving, accelerate, and move through the air fast enough to generate lift. The idea of this experiment is to negate ALL of the airplane's ability to overcome inertia. NOT just 'impede' it, which is what the 'it will take off' people are thinking, but to entirely NEGATE it. This is why chaining it to a wall would be a better iteration of the experiment, because the notion of some kind of 'magic moving conveyor-runway' is absurd, and any attempt to create such a thing would likely fail, or at the very least fail to negate ALL of the plane's attempts to overcome its initial inertia. *IF* (and this is a big if) a plane was on such a 'magic runway', one which was able to fully negate the plane's initial ability to break its stationary inertia, then the FORCE of gravity would in fact prevent the plane from moving forward at all. However, I suspect any actual attempt to actually carry out such an experiment would only see the airplane take off relatively easily, for exactly the reasons people have said - once the plane starts moving, the relationship between the plane and the ground becomes largely irrelevant. But in that case, the experiment would be a failure, because that is NOT what the experiment is about. There are actually all kinds of interesting facets to this kind of thing, from inertia, to center-of-gravity concepts, to countless variables such as relative air pressure, wind heading, etc etc. As said before, this 'experiment' as generally presented does not really explain itself properly, and that is the primary reason for all the disagreement and confusion. On the one hand, it seems (clumsily) set up merely to make the rather basic point that airplanes move themselves differently than automobiles. On the other hand, it actually is really (although probably unknowingly) set up to ask whether or not an airplane can create enough airflow for lift all by itself, without any forward momentum at all - and the overwhelming majority of the time, this answer would be 'no'.
The difference between a conveyor and the Earth is that the air moves with the Earth - it doesn't move with a conveyor belt. That's the reason that if you throw an apple in the air while standing on the Earth (moving 1000mph or whatever), it goes straight up from your perspective. If you throw an apple straight up through the sunroof of your car, it's not coming back down in your car.
Nero, It's not a poorly written riddle. That's just what people who don't get it will say once they realize the conveyor best has nearly zero effect. What? Should it be worded 'If you negate a plane's lift, will it lift off." What kind of riddle would that be? imo, the riddle IS about the conveyor belt or, at least, the wheels vs engines.
haha!! that is the definition of a non sequitor response, imo. ok, i give up. man, you just don't get it.
I think I get where the confusion arises. The spirit of the question is that the conveyor belt will counteract the forward motion of the plane. Even though the engines are going full bore, to an outside observer, the plane is motionless. It has no forward motion, isn't moving through air, won't create lift, and won't take off. But if that's the intention, the wording is poor. The wheels are relatively frictionless. If they were totally frictionless, you could turn on the conveyor belt and the plane would stay in the same place, even without they engines running. And that means the conveyor belt actually has no bearing on anything. When you turn the engines, it would move down the runway as it normally does and take off. So it really depends on how you interpret the question. If you follow to the apparent intention of having a plane staying stationary while the engines running normally, it won't take off. But you attempt to use the flawed logic of using a runway long conveyor belt to accomplish that, the plane will travel down the runway as if were concrete and take off.
To clarify, a conveyor belt can't negate the forward motion of the plane because the wheels have little effect on how the plane moves.
It is a very poor riddle. As you can see, the interpretation of the riddle varies. Its a very vague question with lots of unanswered variables. Its a D&D style question where once can beat his chest and accuse the other they don't understand the question. So yes, the simplified question is, " are you trying to impede or negate a planes forward momentum". It can be read both ways.
In theory, yes it can(before lift). But good luck building a conveyor belt that can keep up with the power of a jet engine.
No, I understand it perfectly. As I said, on the face of it, it is merely a clever way to make the point that airplanes move by generating thrust, thereby pushing the plane through the air, while cars generate momentum by pushing against the ground, and shifting its center of gravity far forward of the vehicle itself, thereby causing the vehicle to move. I know all of that perfectly well. The point is, though, if that is indeed the only point of the riddle, then it's inane, elementary-school stuff, not to mention that if the plane moves forward at all, then the experiment is a failure, because the 'magic conveyor belt' does not actually do what the riddle stipulates. But you're right - if the riddle was worded more clearly, one way or the other, then yes, it would not be much of a riddle. Besides, helicopters long ago proved that you CAN generate lift without forward momentum. Although, technically, the blades of the copter do still move 'forward' through the air, just in a circle.. But no, I am not one of those who 'don't get it'. I get it. I just recognize a poorly-explained experiment for what it is. Along the same lines, here is a similar 'riddle': If you hold a regular egg at a height of 4 feet and drop it, you can prove mathematically that it will never hit the floor. How? Because, when the egg has traveled halfway down, it still has the remainder of the other half to travel before it hits the floor. Then, when it has traveled half THAT distance, it still half of THAT remainder, and so on and so on, into infinity. You can ALWAYS halve the remaining half, to an infinitely small number. Funny thing is, this is absolutely true, and therefore, there is no way the egg should hit the floor. Obviously it will hit the floor, and you would have a mess to clean up. The question is, WHY does it hit the floor, when it should be a mathematic impossibility? It's a similar question to this 'conveyor-belt/airplane riddle'.
Of course the treadmill exerts force. Just stand on a treadmill it will throw you off. The engine works on one plane (X); the treadmill is also operating on the same plane (X) except the opposite direction.
It's not a mathematic impossibility - it will "never" hit the floor only if you stop time. Each time you're going "halfway", you're also going through a smaller period of time. It's not that you're never getting to the floor - you're just not letting time get to the point where it does. Halfway to the floor = 1 second (let's ignore gravity for simplicity) 3/4 way to the floor = 1.5 seconds 7/8 way to the floor = 1.75 seconds The problem is by this measuring strategy, you're never going to get to 2 seconds. So yes, if you don't let time run its course, it will never hit the floor - and that's what would take place in reality too. If you only only allow time to get to 1.999 seconds, the egg will never hit the floor.
If the plane is not moving forward and forcing air over and under the wings it will not lift off. It is like running in place. Now if it is a harrier jet it can angle the thrust downward and take off. DD
The treadmill exerts force but the force it exerts is almost entirely on the wheels causing them to spin on their axles. Very little of this force gets transferred as force opposing the thrust of the planes engines. So the treadmills force will cause the wheels to spin faster, but will impede the forward motion of the plane very little.
if the conveyor belt is turned on before the engines and gets that plane moving at 500mph, the movement through air will create a wind (and lift on the wings) that will send that plane flying even without it's engines on. haha!
Nice try, but no. That's not it. You are correct, however, in one respect, but you are observing an effect rather than a cause. Even if you never stop time, you can still divide the remainder of the remaining time in half just as much as the remaining distance. But I will say, you are on the right track, just need to follow it.
if I tie that plane to a wall, and fire up it's engines to 500 mph and blow a 200 mph wind at it, with absolutely zero forward momentum, just like a kite! haha!
