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Can A Fly Stop A Train?! (more Technical)


boon racoon

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I'll try to explain as I was of the same pov as you.

When a plane moves on normal concrete the wheels move because of the propellor or engines not from their own power source.

So, much like rollerblades/skates on a treadmill they will spin round and round but not effect the speed of the person/plane above.

So if the plane was to power up its engines it would start moving forward anyway, getting the nessicary lift.

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Because if the belt is matching the speed of the plane, it doesn't really matter, because the wheels will just spin a bit faster. It's like standing on a treadmill on rollerskates, whilst pulling on a rope: You'll move forwards.

Obviously that's if the belt was matching the speed of the plane. That's shockingly simple, everyone should understand it. But if the belt matches the speed of the wheels, it's much more interesting and contentious.

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Oooooooooooooooooooooooooooooooooo i get it now.

But...

as the tredmil sped up, to try and equal out the speed of the plane cuased by the engines, the belt would get faster and faster, to infinite speeds, and destroy the wheels, and knock the plan off balance and it wouldn't take off.

Edited by JT!
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ryan leech, revolution, circa 2000

coolest thing ever done

i really really really need to see this!!!!

and to answer your plane theory!

no it wouldn't take off! dont question me, it just wouldn't ok!

and the monty hall sameshow balls, you are best to change cups!

tar night!

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Why oh why oh why are we still arguing the plane thing? I thought we had proved the disbelievers in the thread before.

The plane WILL take off, if you dont think it will, re read the ORIGONAL wording, and google it- all is explained. If you still dont understand something is wrong in your brain.

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why not? (not counting when the plane is actually flying :P )

Well the plane has to be moving through the air at some point, so the belt isn't keeping up with the planes speed. Making the question wrong. :rolleyes:

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Well the plane has to be moving through the air at some point, so the belt isn't keeping up with the planes speed. Making the question wrong. :rolleyes:

why isnt it ? what is stopping that from happening ?

EDIT : FOR GODS SAKE, WILL PEOPLE JUST THINK ABOUT IT ... THE PLANE TAKES OFF

Edited by manuel
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I know it's off topic - which is probably a good thing - but did anyone see the video, I think it was an ad for DC shoes, with a BMXer trackstanding in a carpark and someone drove at him in a go kart with a ramp over the top of it. The bmxer does a backflip without moving forwards. Soooo cool to watch - up there with Ryan Leech manualing down the moving ramp.

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why isnt it ? what is stopping that from happening ?

Well, effectivly, when the planes engines start moving the plane forwards, the blet would speed up and try and equal it out and keep it still, but it wont make a difference, so the belt will get faster and faster, to infinite speeds, but it wont make a difference. So the belt cannot match the speed of the plane, even though the question says it can.

Also, when the belt gets to very high speeds, it will actually start to effect the plane, becuase of the resisitance in the wheels bearings, so, for the belt to keep the plane still (like it says in the question) it'll have to be moving very fast, so really....

...the plane wont take off. :P (So long as we're talking realistically, in theroy it would take off, but that would make the question inaccurate)

Edited by JT!
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Well, effectivly, when the planes engines start moving the plane forwards, the blet would speed up and try and equal it out and keep it still, but it wont make a difference, so the belt will get faster and faster, to infinite speeds, but it wont make a difference. So the belt cannot match the speed of the plane, even though the question says it can.

the belt won't go to infinate speeds though, it will only go as fast as the plane needs to go take off. which is 200ish mph for a 747.

Also, when the belt gets to very high speeds, it will actually start to effect the plane, becuase of the resisitance in the wheels bearings, so, for the belt to keep the plane still (like it says in the question) it'll have to be moving very fast, so really....

The only point the conveyer belt would keep the plane still is when the plane isn't moving. The resistance in the wheel bearings is negilgable and on a normal runway the plane still over comes them and yeah a conveyor belt going at 200mph would probably have some effect on the plane. The plane though will have more than enough power to overcome them and will just require the pilot to give it a bit more pasty to get the plane up to take off speed!

But then the whole question is thoretical and its more of an exercise in lateral thinking, rather than geniune realistic problem!

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I know it's off topic - which is probably a good thing - but did anyone see the video, I think it was an ad for DC shoes, with a BMXer trackstanding in a carpark and someone drove at him in a go kart with a ramp over the top of it. The bmxer does a backflip without moving forwards.

Do you have a video of that? It sounds cool.

Well, effectivly, when the planes engines start moving the plane forwards, the blet would speed up and try and equal it out and keep it still, but it wont make a difference, so the belt will get faster and faster, to infinite speeds, but it wont make a difference. So the belt cannot match the speed of the plane, even though the question says it can.

If the plane is going 100 mph forward, the runway goes 100mph in the other direction. What's hard to understand about that?

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Some people must think the main way to decide somethings speed is by how fast its wheel are spinning.

Thats f**king retarded. What is something doesnt have wheels? Can it not move?

An objects (a plane is an object too) speed is determined by how fast it is moving, not how fast its wheels are spinning.

So when the question says that the conveyor tracks the speed of the plane, it obviously means its speed, Relative to 'not moving at all', which is also an obvious assumption.

So JT, either you think things without wheels cannot move (because they can have no speed), or you're wrong because the question does make sense (to parody your post with a closing question with seemingly obvious answer to prove a point :P )

if the plane does take off, why aren't the navy. etc using this on aircraft carriers?

I hope you are joking. If not well you're a very special boy ^_^

Edited by Extreme_biker0
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I've just been thinking about this..

It's like walking on a treadmill, you're walking the same speed as the belt is moving, but you're not going anywhere, you're in the same place.

If it was like this with the plane, it'd work the same as if the engines etc were all at full blast, but with the plane on the spot.

If my understanding of how planes work is right, then it wouldn't take off, because there's no air being blasted under the wings, making it fly. :ermm: - Well, not enough anyway?

If the plane was actually moving along the conveyor, say 100mph. Then surely this would be the same as it going 100mph normally?

If it couldn't take off at 100mph normally, then what would make it take off at 100mph on a conveyor? - The only difference, is the wheels moving twice the normal speed.

I'm pretty sure the wheel's don't control the drive of the plane, they just sit freely, like our front wheels do.

They just get pushed along by the drivechain.

:S

Thought i'd post this, just for fun. :P - http://video.google.co.uk/videoplay?docid=...amp;q=treadmill

Edited by Dan6061
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I've just been thinking about this..

It's like walking on a treadmill, you're walking the same speed as the belt is moving, but you're not going anywhere, you're in the same place.

If it was like this with the plane, it'd work the same as if the engines etc were all at full blast, but with the plane on the spot.

If my understanding of how planes work is right, then it wouldn't take off, because there's no air being blasted under the wings, making it fly. :ermm: - Well, not enough anyway?

If the plane was actually moving along the conveyor, say 100mph. Then surely this would be the same as it going 100mph normally?

If it couldn't take off at 100mph normally, then what would make it take off at 100mph on a conveyor? - The only difference, is the wheels moving twice the normal speed.

I'm pretty sure the wheel's don't control the drive of the plane, they just sit freely, like our front wheels do.

They just get pushed along by the drivechain.

:S

Oh. My. God. We're back at the square one again...

The wheels are frictionless, so whether the conveyer is going at 1000 knots forwards, backwards, or not moving at all it will have no effect on the plane at all. As far as the plane is concerned it is just going on a normal runway so will be able to take off in the usual way.

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oh my god!!!111!1!1 this plane has no wheels.

IPB Image

good man!

how do people not get this? does a plane get propulsion from air shoved out the back of the engines? or the road underneath it? because if its the latter, how in the hell do they keep movin in the sky?

right, i'm sure some people won't even understand this. i'm on a mission for visual proof, to shut them up and let this thread tumple to the depths of hell. not calling anyone stupid. i just don't see how some people are still not seeing it after all the wonderfully blatant explanations that have been posted

smithy

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I wantd to prove it myself, but i got a report to write. so read up munchkins and tell all us clever people your sorry

Airplane on Conveyor Belt - Deconstructed

Posted by Swood having to do with Riddles

I have been doing a lot of thinking and research into the "Airplane on a Conveyor Belt" conundrum. For some reason, I find this thought experiment to be extremely compelling. You can tell a lot about a person's thought process (and background) by the way they defend their position. It really is amazing.

As I've said previously, this problem tends to divide people radically. There are some people (very few) who just "get it" right from the start. Then there are those who believe that their initial, intuitive answer must be the right one... there's just no other way. I must admit that I was in the camp that immediately said "no way, that thing can't possibly fly... it's obvious!" Eventually, after giving the problem at lot of though, I finally understood what was going on.

The Problem:

An aircraft is standing on a runway that can move (a conveyor belt). The aircraft moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the aircraft's speed and tunes the speed of the conveyor to be exactly the same, but in the opposite direction. There is no wind. The pilot begins to add thrust to the engines...

The question is:

Will the plane take off or not?

The Result:

Yes, the aircraft will proceed down the conveyor-belt runway in exactly the same way it would down an asphalt runway. It will take off as normal. If you were watching from the sidelines, the take-off roll would look identical to any other that you may have seen. The only difference being the rate at which the wheels are spinning. They would be spinning approximately twice as fast.

The aircraft does not suddenly lift vertically (like an elevator) as some proponents of the "No, it won't fly" camp seem to think we are proposing. That would be physically impossible, assuming no wind.

The Assumptions:

In order to avoid any messiness, let's make one basic assumption.

1. Let's assume no friction at the wheel hubs. ie... the aircraft wheels can spin as fast as they want.

This isn't a deal breaker or a shortcut, in fact, it's not really even necessary. It is merely a way to dismiss the completely irrelevant argument that "there's no way an aircraft's wheels could spin 500mph without burning up." Yeah, that's fine... but it has no relevance in our thought experiment. Nobody is going to build a giant runway conveyor belt either.

The Solution:

Here are the keys to understanding this problem:

1. The wheels of an aircraft are "free-wheeling". They do not provide propulsion, and therefore do not "push against" the action of the conveyor belt.

2. The thrust for aircraft movement comes from jet engines or propellors... not the wheels. Therefore, the thrust being applied to the aircraft body is completely decoupled from how fast the wheels happen to be spinning.

3. Thrust acts according to Newtons Third Law of Motion - every action has an equal and opposite reaction. The thrust of the engines is acting against the air.

Because the wheels are free-wheeling and we have assumed zero friction at the hub, it follows that the conveyor belt, no matter how fast it is moving, CANNOT EXERT ANY FORCE on the aircraft with respect to forward motion! There is no force in our experiment that can oppose the thrust vector of the aircraft.

If the conveyor belt cannot exert any relevant force on the aircraft, you can completely ignore it. Ergo, the aircraft takes off as if nothing unusual is happening.

Addressing Some Common Arguments:

1) "The conveyor belt will cancel out any forward motion of the aircraft. The plane will not move at all."

Short Answer: The belt has no way to exert force with respect to the forward motion of the aircraft. All it can do is make the wheels spin faster or slower.

Long Answer: Your conditions are illogical.

* You claim that the aircraft will not move

* If the plane doesn't move, then the conveyor belt doesn't move either

* If the belt is not moving, then how is it cancelling any forward motion of the aircraft?

2) "The plane will remain stationary, but will lift into the air... thus taking off."

Answer: This is an aerodynamic impossibility (assuming no wind), which should be obvious.

3) "But if you said the the conveyor belt matches the speed of the WHEELS, it wouldn't be able to take off."

Short Answer: See Argument #1.

Long Answer: Once again, your conditions are illogical. The conveyor belt can never "match" the speed of the wheels unless the aircraft does not move. With a tremendous thrust vector behind it with no opposing force, the aircraft will move. Once the aircraft begins to move, we enter into a paradoxical situation.

* X = Wheel Rotational Speed

* X = Conveyor Belt Speed, as per your conditions

* Z = Speed of Aircraft = Some non-zero positive number

The equation is: X = X + Z, which is illogical.

Example. The aircraft is moving 10mph (X = X + 10) with the wheels rotating at 10mph. Therefore, the belt must react and accelerate to 10mph. But now the wheels are rotating at 20mph... and so on to infinity.

4) "You can't just ignore the conveyor belt as you claim. Take this situation for example..."

A guy is standing on the conveyor. He sees a plane moving forwards away from him at 10mph on the conveyor. He also knows that the conveyor itself is also moving at 10mph in a forwards direction. The total velocity of the plane in relation to the ground must be 20mph.

If the conveyor can be ignored then why is the plane's total velocity twice what it would normally be if it was moving along on tarmac.

The fact that you cannot explain this indicates that you've either ignored or overlooked some of the forces at play between the conveyor and the plane.

I don't see any violations.

You state that the aircraft is moving 10mph relative to the conveyor (perhaps as measured by a speedometer on the wheels). The conveyor itself is moving 10mph relative to the ground in the same direction. The total speed of the aircraft relative to the ground (tarmac) is 20mph.

I don't see any problem with this. Ignore the conveyor by making it pop out of existence and you suddenly have an aircraft traveling down the tarmac at 20mph.

You can change your point of view as much as you like, but you still end up with an aircraft traveling 20mph with respect to the ground.

References and Further Investigation:

The Straight Dope - "An airplane taxies in one direction on a moving conveyor belt going the opposite direction. Can the plane take off?"

AVWeb.com - Pilots Lounge #94 - "Conveyor-Belt Runway"

Airliners.net Tech Ops - "If A Plane Took Off A Conveyor Belt..."

Tempus Fugit Blog - "Airplane on a Conveyor Belt"

PhysOrgForums - 275 pages of discussion!!!

click here

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Dear me... the plane is powered by jet stream and not through the wheels.

As long as the wheels withstand the speed with which they need to turn, what's the problem?

Some really retarded thinking here... :S

And coming back to the train and fly thing, even if a fly had the same kinetic energy as the train it wouldn't stop it but punch straight through it. It's like shooting a bullet at a train, it won't slow it down.

Sorry if these conclusions have been reached, 8 pages is too much to read through.

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Right then. Forget flys and planes, watch this - (sorry not a link, I'm not that clever) go to 'www.dcshoes.com' then 'videos' then 'bmx' then under footage is one titled 'Colin Winkelmann - Go-kart backflip'. Watch it!

Plane takes off and the fly would die so I doubt it'd be bothered about the train any more.

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