A harmless little riddle

The plane is hijacked by terrorist, but as soon as it takes off it crashes because the experiment was done in a vacuum.

i thought this was a harmless riddle... there's going to be waaaaaaaaaaaaaaaaaar!!

Congratulations.

You have found the perfect way to start a fight.

Pherekydes wrote:

Here's the quote:

Pherekydes wrote:

The engines push against the air. The engines move forward.

The engines push against the air. The engines do move forward.

They push against the air. They do NOT move forward. How hard can it be to understand this?

the riddler wrote:

An airplane is sitting on an enormous treadmill. As the plane starts its engines, the treadmill runs in the opposite direction at the same speed the plane is moving. Can the plane take off?

Way to be a douchepump. I wank to pics of your mom.

????? wrote:

They push against the air. They do NOT move forward. How hard can it be to understand this?

If they push against the air, how can they not move forward?

How hard can it be to understand this?

A balloon pushes its air out and it moves in the opposite direction. An engine pushes its air out and moves in the opposite direction. Anybody who has ever attended even a basic lecture on jet engines or aerodynamics has seen this example. Even a 6 year old can understand this when shown the balloon example.

wow, this thread has gone on for way to long...

just looking at this thread reminds me of a monty pyhton skit where he pays a guy to argue w/ him.

http://video.google.com/videoplay?docid=-572077907195969915&q=monty+python

Dammit, we just lost a bunch of posts. I thought we were making progress too.

no

This is getting silly.

First of all, as I'm sure has been mentioned in this thread, the plane is moving. This is stated in the riddle in the part where it says "the plane is moving". Now you'll counter with, "the treadmill runs in the opposite direction at the same speed." The same speed as what? The forward movement of plane. If the plane moves forward, as is stated in the riddle, it can take off. Now we have answered the riddle as worded. Remember it's a riddle, not a scientific question.

However, you may be able to build a semantic argument whereby you say that what the riddler meant to say is that "the treadmill spins so fast that it negates any thrust acting on the plane so as to stop any forward movement." Although this eliminates the wording of the original riddle, it is still possible for the now stationary plane to "take off"...

I propose the following explanation of the scenario. Feel free to slam my analysis:

Friction - There must be some friction between the treadmill and wheels of the plane. This is an important concession because it admits that the treadmill can exert a force on the plane. There is also friction between the wheels and bearings/axels of the plane, but this is less important. This is different from the utilization of friction in walking or driving as was mentioned above. Planes and rockets are propelled by the conservation of momentum, not by applying force to a stationary surface in order to cause and equal and opposite normal force. Planes CAN take off from a frictionless surface.

Boundary layer theory - I believe this aspect of the situation has yet to be addressed in this thread. You'll have to consult your Fluid Mechanics or Transport Phenomena textbook for the specifics, but boundary layer theory means, in this case, that the moving treadmill will create movement in the layer of air just above it, which means a substantial wind will be created above the surface of the treadmill at high treadmill velocities. You can test this for yourself by placing your hand just above a moving treadmill. This wind will pass around the wings, which, by bernoulli's principle, creates lift causing the plane to lift off of the treadmill in the same way as if the plane were in a wind tunnel. This requires, of course, extreme treadmill size and rotational velocity, but I think it is implied in the riddle that we're dealing with no ordinary treadmill. Now, it's up to you whether this constitutes a "take-off" or not.

This is what happens when you're lab equipment is screwed up and you have nothing to do...

ok, let's get this straight. the wheels of an airplane are not free-spinning. if you think they are, go up to one and give it a big spin, like you were on the price is right. gravity is pressing the wheels of the plane to the runway/treadmill. it's not like some giant hand is holding the airplane up while the treadmill spins the wheels beneath it, and the plane is free to accelerate due to the force of its engines. until the plane reaches a speed that can produce enough lift to overcome gravity, it is still being supported by its wheels.

as i referenced before, a fully loaded 747 has a takeoff weight of somewhere around 800,000 pounds. its four engines are each rated at approximately 60,000 pounds of thrust each, for a total of 240,000 pounds of thrust. this is the difference between an airplane and a rocket. the airplane's engines alone are not powerful enough to lift the airplane off the ground. that is why it must accelerate on the ground to a speed fast enough to produce the necessary lift. THE ENGINES OF THE PLANE DO NOT HOLD IT SUSPENDED IN THE AIR, IT'S WEIGHT IS ON THE WHEELS.

wow. wrote:THE ENGINES OF THE PLANE DO NOT HOLD IT SUSPENDED IN THE AIR, IT'S WEIGHT IS ON THE WHEELS.

This doesn't change with the addition of the treadmill, though. You're still simply supporting the weight of the plane until the plane is going fast enough down the runway to generate enough lift to take off.

All that changes is that the wheels of the plane are going to be rotating faster to compensate for the added movement of the treadmill. The plane still pushes itself through the air and, when going fast enough to generate lift, takes off.

If you're arguing that the added friction generated by the wheels moving faster is enough to stop the plane, well, that's a.) not gonna happen b.) arbitrary and c.) against the original point of the riddle, which is that a plane pushes itself through the air.

I can't say it enough:

The plane pushes itself through the air.

The plane pushes itself through the air.

The plane pushes itself through the air.

The plane pushes itself through the air.

The plane pushes itself through the air.

Think about it.

you are an idiot.

the plane pushes itself ALONG THE GROUND until it reaches take off speed.

there is no imaginary rope that the plane is pulling itself along. its weight is on the wheels. the wheels are on the treadmill. the engines cannot lift the plane off the ground.

think about it.

Oh man. How does an airplane fly? It flies because the engines are pushing air like crazy to generate thrust to make it lift off. This is your 'rope' pulling (really pushing the aircraft).

You're the idiot. Don't ever do anything which will affect anyone. You'll get it wrong.

guesser wrote:

of course not. a plane develops lift from the air traveling over the wings.

The very first response was correct but this has gone on for 30 pages!

No air moving over the wings means no lift, no flight. Just a lot of noise and wasted airplane fuel.

mandingo wrote:

guesser wrote:

of course not. a plane develops lift from the air traveling over the wings.

The very first response was correct but this has gone on for 30 pages!

No air moving over the wings means no lift, no flight. Just a lot of noise and wasted airplane fuel.

Ah, but the problem is that you (and the first post) is wrong. The plane does in fact take off.

mandingo wrote:

The very first response was correct but this has gone on for 30 pages!

No air moving over the wings means no lift, no flight. Just a lot of noise and wasted airplane fuel.

Dude, just stay out of this. Especially if you didn't read the thread.

DK wrote:

mandingo wrote:

The very first response was correct but this has gone on for 30 pages!

No air moving over the wings means no lift, no flight. Just a lot of noise and wasted airplane fuel.

Dude, just stay out of this. Especially if you didn't read the thread.

Absolutely not. I did read through most of them.

I'll make it even easier,

a runway at LAX is converted to a giant treadmill. As the plane starts increasing engine speed the belt increases in speed so relative to a palm tree on the side the plane is not moving forward. Wheels are spinning. What would the plane do? Levitate up? No moving air over wings means no flight. I totally agree about the lack of consensus post.

mandingo wrote:

What would the plane do? Levitate up?

What if the plane is a V-22 Osprey?