No one is claiming it can (other than Row1and, who is completely wrong).
It takes off because it is still moves forward.
No one is claiming it can (other than Row1and, who is completely wrong).
It takes off because it is still moves forward.
congratulations to edro for being the first poster to resort to insults in this entire thread. "are you on crack?" is the bit i mean. meh. Anyway.
We all knkow that thrust doesn't equal lift. THrust does equal forward motion however, and that forward motion equals airflow over the wings which will generate lift.
Consider a firework? OK? please, consider a firework.
Imagine you've put some little wheels on it. or big wheels, it's up to you, but fact is, they're just inanimate wheels. if u spin them, they'll spin for a bit. that's it. ok? do we have that in our minds now?
So, let us pretend that this rocket has some minor aerodynamic foil that prevents it from taking off, and keeps it on the ground.
Now, if you lit that firework, and it was on the conveyer in this question, do you honestly think that it wouldn't move? Seriously? That is what you are argueing saying the plane won't take off.
Imagine someone shot a bullet at you, there is no rifling in the barrel, it just travels at the same orientation, it doesn't spin round. Pointlessly, they've stuck some little wheels on the bottom of it. For fun. Meh, let's say it's going through a vacuum, so there's no air resistance. According to your thinking, if this bullet (say it's travelling at a mere 500mph) with its little wheels on, was to have its wheels meet a treadmill going in the opposite direction at 500mph, that it would be held in place? That is ridiculous.
Go pick up a toy car. Now. DO IT.
Holding it in your right hand and hold your arms out to either side, bring your arms towards each other at the same speed, and run the wheels of that toy car over your left palm. Notice that effectively, the car is briefly on a treadmill going in the opposite direction when its wheels run over your palm. Does this stop it from moving? No. it doesn't. At all. it just makes the wheels spin faster. This is because the force moving the toy car forward, your right hand, is independent of your left hand. Like the thrust of a plane and the conveyer.
Honestly, i can't think of a simpler analogy.
We all knkow that thrust doesn't equal lift. THrust does equal forward motion however, and that forward motion equals airflow over the wings which will generate lift.
Consider a firework? OK? please, consider a firework.
Imagine you've put some little wheels on it. or big wheels, it's up to you, but fact is, they're just inanimate wheels. if u spin them, they'll spin for a bit. that's it. ok? do we have that in our minds now?
So, let us pretend that this rocket has some minor aerodynamic foil that prevents it from taking off, and keeps it on the ground.
Now, if you lit that firework, and it was on the conveyer in this question, do you honestly think that it wouldn't move? Seriously? That is what you are argueing saying the plane won't take off.
Imagine someone shot a bullet at you, there is no rifling in the barrel, it just travels at the same orientation, it doesn't spin round. Pointlessly, they've stuck some little wheels on the bottom of it. For fun. Meh, let's say it's going through a vacuum, so there's no air resistance. According to your thinking, if this bullet (say it's travelling at a mere 500mph) with its little wheels on, was to have its wheels meet a treadmill going in the opposite direction at 500mph, that it would be held in place? That is ridiculous.
Go pick up a toy car. Now. DO IT.
Holding it in your right hand and hold your arms out to either side, bring your arms towards each other at the same speed, and run the wheels of that toy car over your left palm. Notice that effectively, the car is briefly on a treadmill going in the opposite direction when its wheels run over your palm. Does this stop it from moving? No. it doesn't. At all. it just makes the wheels spin faster. This is because the force moving the toy car forward, your right hand, is independent of your left hand. Like the thrust of a plane and the conveyer.
Honestly, i can't think of a simpler analogy.
Ok, am I right in thinking that the conveyor and the wheels of the plane will be constantly increasing to an infinite speed as the plane begins to move forward until it is no longer on the conveyor or it leaves the ground?
Skateboard picture
Here's another one...
What happens when the fan is plugged in? Does the skateboard move?
(Pretend that the cord doesn't impede movement at all)
Here's another one...
What happens when the fan is plugged in? Does the skateboard move?
(Pretend that the cord doesn't impede movement at all)
Sort of. The wheels and will be moving twice as fast as normal. Say the belt moves back at 100 knots and the plane is moving forward relative to the earth at 100 knots. That's a 200 knot difference being noticed by the wheels. The belt and wheels won't accelerate to infinity because the acceleration stops once the plane is airborne. The wheels will be moving at twice the speed of the belt.
no. the conveyer speed is relative to the plane. If it was relative to the wheels, it would lead to a paradox, whereby they instantly accelerated to an infinite speed. even in magic physics land that isn't the case.
the speed of the conveyer is relative to the plane. everyone must accept that as it is in the question. it is in one of the defined parameters of the question. no-one can realy deny that ok? simple.
The speed of the plane is relative to bob, the air, that guy next to the runway, the casual observer. The speed of the plane can't be relative to the conveyer.
Would ou like to know why it isn't relative to the conveyer?
Let's pretend it is. Plane goes at 1mph. conveyer now goes at 1mph also yes? in opposite direction. so now, relative to the conveyer, the pane is in fact going at 2mph. so now conveyer is at 2mph. but holy swiss cheese batman, plane is now relative to conveyer going at 4mph. this will lead to a paradox. so yes, plane speed is relative to some observer in the controltower let's say.
So, we've accepted that the speed of the conveyer is relative to the plane, as the question says so, and we've accepted that the speed of the plane is relative to the the observer, as if it was relative to the conveyer, we meet a paradox.
So, for your conveyor to be moving AT ALL, then the plane must be moving already.if it is moving, then it is clear that the conveyer can't stop it from accelerating as it had to accelerate from rest. The conveyer can't speed up to try to oppose the plane and stop the plan from speeding up, because the conveyer speed is relative to the plane, so if the conveyer has sped up, the plane must have too.
You cannot argue theplane can't take off and mention the convyer moving. Your only argument is as armitage constantly says, to prove that the non moving conveyer has a force that can oppose the thrust of the engines.
so give us one.
the speed of the conveyer is relative to the plane. everyone must accept that as it is in the question. it is in one of the defined parameters of the question. no-one can realy deny that ok? simple.
The speed of the plane is relative to bob, the air, that guy next to the runway, the casual observer. The speed of the plane can't be relative to the conveyer.
Would ou like to know why it isn't relative to the conveyer?
Let's pretend it is. Plane goes at 1mph. conveyer now goes at 1mph also yes? in opposite direction. so now, relative to the conveyer, the pane is in fact going at 2mph. so now conveyer is at 2mph. but holy swiss cheese batman, plane is now relative to conveyer going at 4mph. this will lead to a paradox. so yes, plane speed is relative to some observer in the controltower let's say.
So, we've accepted that the speed of the conveyer is relative to the plane, as the question says so, and we've accepted that the speed of the plane is relative to the the observer, as if it was relative to the conveyer, we meet a paradox.
So, for your conveyor to be moving AT ALL, then the plane must be moving already.if it is moving, then it is clear that the conveyer can't stop it from accelerating as it had to accelerate from rest. The conveyer can't speed up to try to oppose the plane and stop the plan from speeding up, because the conveyer speed is relative to the plane, so if the conveyer has sped up, the plane must have too.
You cannot argue theplane can't take off and mention the convyer moving. Your only argument is as armitage constantly says, to prove that the non moving conveyer has a force that can oppose the thrust of the engines.
so give us one.
This is the wrong analogy. the fan is sitting directly on the skateboard, so there is a large amount of friction present. An airplane does not sit directly on the runway (or conveyor). It's on WHEELS. Try putting the fan on wheels and then put that assembly on the skateboard. Either the fan will push itself off the back of the skateboard, or if the fan is fixed in position (as the conveyor belt would be) then it would push the skateboard out from under it.
The wheels is what makes the difference here because they remove 99% of the friction that would otherwise keep the plane form moving.
Please quote the first post in the discussion and show us exactly where it says this.
I think you need to re-read the question - it never mentions anything about thrust. Just speed.
The conveyer CANNOT contribute any force in opposition to the engine thrust - with the exception of the wheel rolling resistance which we've already established doesn't differ significantly from that of a normal takeoff.
I wasn't saying that it is the same. I already know that the plane takes off. I was just saying that it is something else that we could discuss.
Originally posted by: letdown427
but that isn't very interesting as we all know that that wouldn't work.
Bzzzt! Try again.
I havnt read all of the crazy responses in this thread yet so this may have already been pointed out...
First look at how the conveyer belt acts on the plane.... Assume that the conveyer belt is moving 300 mph backwards..... I would not imagine that the plane would be moving in reverse at 300 mph.... assume that the wheels are almost perfectly frictionless.... the plane would remain mostly stationary and when thrust is applied it would move forward, and the wheels would spin at 600 mph.
Another way to look at it, the plane is sitting directly on the coveyer belt, the body right on it... the 300 mph belt moves it backward at 300mph, but as soon as friction is broken it would accelarate from -300mph to whatever speed the thrust would put it at.
First look at how the conveyer belt acts on the plane.... Assume that the conveyer belt is moving 300 mph backwards..... I would not imagine that the plane would be moving in reverse at 300 mph.... assume that the wheels are almost perfectly frictionless.... the plane would remain mostly stationary and when thrust is applied it would move forward, and the wheels would spin at 600 mph.
Another way to look at it, the plane is sitting directly on the coveyer belt, the body right on it... the 300 mph belt moves it backward at 300mph, but as soon as friction is broken it would accelarate from -300mph to whatever speed the thrust would put it at.
100 mph of the conveyer moving backwards would only translate into a net few mph because of the minimal amount of friction on the wheels
so if the conveyer is moving at 100mph plane puts enough thrust to move it at 100mph. in reality the plane will be moving 99 mph forward or something similar
so if the conveyer is moving at 100mph plane puts enough thrust to move it at 100mph. in reality the plane will be moving 99 mph forward or something similar
Originally posted by: juiio
Originally posted by: letdown427
but that isn't very interesting as we all know that that wouldn't work.
Bzzzt! Try again.
Either you're going to tell me that the white board falls over or blows away, or that that somehow works, and the skateboard moves.
The only way I can see that moving is the skateboard would move backwards(to the fan end) becaus the white board wouldn't capture all of the air?
Otherwise it would seem on first impressions that surely it can't be propelled forwards (towards the white sheet) as it would seem that the fan blowing air forwards would push the skateboard backwards, and this would be counteracted by the air pushing the white panel, thus pushing the skateboard forwards, and cancelling it all out.
I presume you have seen this in a lecture or something and it in fact works contrary to first impressions?
Meh, my firs tthought would be either it stays still in theoretical physics world, but RL it moves slightly backwards (fan end) as the white sheet doesn't feel the force of all the air.
Please enlighten me!
And yes, whilst you can try and thread jack (the 0.999...=1 jacking has been beaten) ultimately, people will read the topic and bluntly propse their it cant take off opinion without reading the thread, and it will eventually be steered back on course
So
Lifer
- Jul 2, 2001
- 25,923
- 17
- 81
Originally posted by: letdown427
Originally posted by: juiio
Originally posted by: letdown427
but that isn't very interesting as we all know that that wouldn't work.
Bzzzt! Try again.
Either you're going to tell me that the white board falls over or blows away, or that that somehow works, and the skateboard moves.
The only way I can see that moving is the skateboard would move backwards(to the fan end) becaus the white board wouldn't capture all of the air?
Otherwise it would seem on first impressions that surely it can't be propelled forwards (towards the white sheet) as it would seem that the fan blowing air forwards would push the skateboard backwards, and this would be counteracted by the air pushing the white panel, thus pushing the skateboard forwards, and cancelling it all out.
I presume you have seen this in a lecture or something and it in fact works contrary to first impressions?
Meh, my firs tthought would be either it stays still in theoretical physics world, but RL it moves slightly backwards (fan end) as the white sheet doesn't feel the force of all the air.
Please enlighten me!
And yes, whilst you can try and thread jack (the 0.999...=1 jacking has been beaten) ultimately, people will read the topic and bluntly propse their it cant take off opinion without reading the thread, and it will eventually be steered back on course
No, what he's saying is that your metaphor doesn't apply to the physics question at hand. The engines aren't acting on the conveyor belt, but the air around the plane.
Bingo :thumbsup:
It isn't relevant to the plane question (the plane does take off), but I didn't see any reason to start another physics thread.
The speed of the plane is independent of the wheels. They are free spinning. The conveyor belt can spin as fast as it wants, and the plane wheels will just spin faster.
I repeat, can someone use physics to prove that the plane doesn't move? I have seen many people say it doesn't move, but no one uses physics in their reasoning.
People... the conveyor belt does not stop the plane from moving, it just makes the wheels spin faster. They can break off and skid, but the plane will move foreward. Think of it the same as if you were sitting on a computer chair with wheels. And somehow magically if you get going 5 mph you will take off. Well... you arent spinning the wheels. You are pulling a rope. The wheels will spin really fast, but you can always pull yourself with that ropeand get going. The air is the rope, and the engine is your arms. Make sense yet?
fvck no it won't take off, there will be no lift.
Tire speed has nothing to do with a plane.
I can't believe "your group" was torn down the middle on this.
kd
Tire speed has nothing to do with a plane.
I can't believe "your group" was torn down the middle on this.
kd
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