A harmless little riddle

It will take off if it maintains the 150mph and makes a large 180 degree turn so that it is now feeling the rush of 300mph winds under its wings. This is possible on an enormous treadmill if it started at the right end.

(Now that there have been so many replies to this thread, I take it that this has already been typed?)

You incorrectly believe that the airplane needs to push off of a ground surface to attain take-off velocity.

It pushes off of the air around it, which is not affected by the moving treadmill.

I read most of the thread and let me offer the perspective of a complete dumbass who's never taken a physics class in her life. Apparently the plane flies. Does it do so because... A. The wheels are free so the plane stays basically in place without the engines on no matter how fast the treadmill goes pretty much. Would that sort of be like a car getting tested on a dyno? Or is it B. The speed of the treadmill is equal to the plane but the force is more powerful to make the plane go this speed than it is to make the conveyor belt move at the same speed? I cant think of an analogy for this one but the clearest explanation was about how the speedometer of a car saying 30 when its going up a hill despite it really being 15 or so. Or is it a combination of both, or neither?

Please try to keep the insults to a minimum I'm just trying to learn a little.

If the treadmill is replaced by an aircraft carrier travelling in the water, then the doubters on this thread must accept that no aircaft would ever take off from the vessel.

The facts proves them wrong!

XC Runner wrote:

If the treadmill is replaced by an aircraft carrier travelling in the water, then the doubters on this thread must accept that no aircaft would ever take off from the vessel.

The facts proves them wrong!

i think you would consider the speed the aircraft carrier is traveling in the water neglidgable compared to how fast the plane travels (meaning the plane could go fast enough so that the speed of the aircraft carrier is overcome). it certainly wouldn't cancel out air resistance like in the scenario that's being discussed now. planes taking off from aircraft carriers are definately faster quicker than anything most people will ever fly in. does this riddle refer to a commercial airline plane or some military jet?

What the hell is wrong with you? Have you even read anything that has been said? THE PLANE DOES NOT STAY IN THE SAME POSITION! IT MOVES FORWARD AND TAKES OFF NORMALLY! Noone is arguing that a stationary plane can take off, so don't waste people's time by continuing to write that.

duk_e wrote:i think you would consider the speed the aircraft carrier is traveling in the water neglidgable compared to how fast the plane travels

Who said anything about the plane being a commercial airline or some military jet?

The plane could be a microlight with a take-off speed equivalent to the speed of an aircraft carrier.

The microlight would still be able to take-off from the moving aircraft carrier.

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?

The riddler wrote "the plane is moving".

Ergo the plane can take off.

If the plane was stationary on the treadmill,

then the treadmill would also have stopped.

I honestly cannot believe that this thread has lasted this long. An article on one of the earlier pages showed why it would take off. Go back and read it.

The treadmill cannot stop the plane from moving forward.

To someone who believes the plane will not take off, please explain in detail why it will not.

p.s. What speed does the earth revolve at? Think about why I asked this question before you reply.

He did not write the 'plane is moving'. he 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'

He wants us to assume the treadmill is moving. he said the plane is SITTING on a treadmill, nothing about the plane moving. The engines starts, THEN the treadmill runs in the opposite direction at the same speed the plane is moving. The plane WAS NOT moving, therefore, the treadmill is not moving either.

Nothing is moving, nothing is taking off.

You are on a treadmill, and you reach forward and grab the bar and let your feet drag.

Does the treadmill throw you off the back? Unless you have very weak arms...no. Why? Because you are grabbing the bar, exerting force there, and that force is greater then the force tugging your feet backwards.

Now imagine if there was another bar farther ahead and another beyond that, suspended over the treadmill. You could drag yourself forward like we used to do on the monkeybars at school, and the slight tug backwards by the treadmill at your feet wouldn't stop you much.

The plane is the same principal. The plane is grabbing onto the air like monkeybar handles. The tug at its wheels backwards is negligible. The plane pulls itself forward by grabbing the air and dragging its feet (wheels).

As long as the runway/treadmill is long enough, the plane will take off

Concerned wrote:

He did not write the 'plane is moving'. he 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'

He wants us to assume the treadmill is moving. he said the plane is SITTING on a treadmill, nothing about the plane moving. The engines starts, THEN the treadmill runs in the opposite direction at the same speed the plane is moving. The plane WAS NOT moving, therefore, the treadmill is not moving either.

Nothing is moving, nothing is taking off.

i agree. at 150 mph (exactly opposite the treadmill) and not moving, the plane will not take off. If the treadmill is large enough for the plane to overcome the -150 (300 mph in respect to the treadmill but only 150 mph in respect to the air) than i think it can. Provided that it can go that fast, which i question. i have no idea how fast planes need to go to get off the ground though. (but i'm assuming then can't do 300 mph on the ground????)

Concerned wrote:He did not write the \'plane is moving\'. he 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\'

He wants us to assume the treadmill is moving. he said the plane is SITTING on a treadmill, nothing about the plane moving. The engines starts, THEN the treadmill runs in the opposite direction at the same speed the plane is moving. The plane WAS NOT moving, therefore, the treadmill is not moving either.

Nothing is moving, nothing is taking off.

If neither the plane nor the treadill was moving and the engines of the plane were started then the plane would start to move down the treamill i.e. exactly the same situation as on a normal runway.

If the treadmill is now started up and matches the speed of the plane then the wheels of the plane would spin faster. The plane would ned to gerenate sufficient power to overcome the friction losses between the wheels and the treadmill and any frictional losses in the wheel bearings.

These losses are very small.

The treadmill cannot now stop the plane or move it backwards.

The treadmill would need to exert a force on the plane to ovecome the forward power of the engines. The points of contact between the plane and the treadmill are the free-spinning wheels and the frictional forces of the wheel- bearings are very small compared to the forward thrust of the plane.

The speed of the treadmill is therefore irrelevant and the plane will continue to accelerate forward until it starts to fly at normal take-off speed.

This thread has legs. Great riddle. Part of the reason is that many of the people who are right may not know what they are talking about.

My wife had the right answer but didn't think the plane would be moving forward. The problem is counterintuitive which makes it so intersting.

i can't stop laughing at all the people picturing a plane sitting motionless on a giant treadmill moving so fast that that it is able to counterract the thousands of newtons of force produced by the jet engines. the only way the treadmill can produce a force in the opposite direction of the propulsive force is to spin the wheels backwards, considering the negligible friction between the wheels and the axle thanks to bearings, the speed the treadmill would have to be moving would be much, much greater than the speed of the plane in order to produce a force equal to that of the jets in the opposite direction. the situation, most of you are picturing is impossible

ned plimpton wrote:

i can't stop laughing at all the people picturing a plane sitting motionless on a giant treadmill moving so fast that that it is able to counterract the thousands of newtons of force produced by the jet engines. the only way the treadmill can produce a force in the opposite direction of the propulsive force is to spin the wheels backwards, considering the negligible friction between the wheels and the axle thanks to bearings, the speed the treadmill would have to be moving would be much, much greater than the speed of the plane in order to produce a force equal to that of the jets in the opposite direction. the situation, most of you are picturing is impossible

The Riddler said that the treadmill MATCHES the speed of the plane "in the oppisite direction"... The plane is therefore not moving in relation to the ground (and more importantly, not moving through the air...)... THEREFORE... NO CAN FLY...

A similar riddle would be: Anchor the plane to the ground with a long, very strong cable. Let the plane slowly move forward until the cable is "tight". Will the plane take leave the ground if the engines are slowly advanced to full power? (The cable will not break.)

Braavo Furgi wrote:The Riddler said that the treadmill MATCHES the speed of the plane "in the oppisite direction"... The plane is therefore not moving in relation to the ground (and more importantly, not moving through the air...)... THEREFORE... NO CAN FLY...

A similar riddle would be: Anchor the plane to the ground with a long, very strong cable. Let the plane slowly move forward until the cable is "tight". Will the plane take leave the ground if the engines are slowly advanced to full power? (The cable will not break.)

The plane is NOTanchored to the ground.

The treadmill can be moving at ANY speed (zero speed, same speed as the plane or ten time the speed of the plane) and it will have not effect on the plane which will continue to accelerate down the treadmill until it takes-off.

Braavo Furgi wrote:

A similar riddle would be: Anchor the plane to the ground with a long, very strong cable. Let the plane slowly move forward until the cable is "tight". Will the plane take leave the ground if the engines are slowly advanced to full power? (The cable will not break.)

The treadmill is not anchoring the plane.

Recall, the only point of contact between plane and treadmill is the tyres. And they are free to rotate.

So it's not similar at all. You can rotate the wheels of an aircraft by hand.

Lift is created by speed relative to the air, not the ground.

Thank you everyone for a good thread.