A harmless little riddle

spikemandc wrote:

You're driving a plane down a runway at a constant 50mph. The second half of the runway is a treadmill spinning at a contant 50mph. What happens when the plane reaches the treadmill? I think it will stop and would invite other points of view.

This is what would happen:

1) If the treadmill was spinning in the direction OPPOSITE of the direction of the plane, the PLANE RELATIVE TO THE EARTH would continue to travel, while the TANGENTIAL VELOCITY at the tire/treadmill interface would rise to 100 MPH.

2) If the treadmill was spinning in the SAME DIRECTION as the direction of the plane, the PLANE RELATIVE TO THE EARTH would continue to travel at 50 MPH while the TANGENTIAL VELOCITY at the tire/treadmill interface would fall to 0 MPH.

Simple as that.

Well, in reality, the plane would probably spin out of control due to its relatively narrow wheelbase, but I don't think you want to get into a vehicular dynamics discussion with me.

CORRECTION:

#1 should read:

1) If the treadmill was spinning in the direction OPPOSITE of the direction of the plane, the PLANE RELATIVE TO THE EARTH would continue to travel at 50 MPH, while the TANGENTIAL VELOCITY at the tire/treadmill interface would rise to 100 MPH.

spikemandc wrote:

A vote for "No" with some input from my aerospace engineer dad.

PLEASE tell me you were lying about "input from my aerospace engineer dad."

I don't think I could ever fly again if there truly are aerospace engineers who cannot comprehend this.

The plane would never stay on the treadmill. The big blades spinning push the air behind the plane and cause the palne to move forward. All the wheels do is make it so a plane isnt a piece of metal sitting on the ground. So once the engines are going, the plane is moving forward regardless of the ground under it. The treadmill spinning backwards would have no effect on the plane because the wheels rotate freely.

Eritrea?WhatsThat wrote:

The plane would never stay on the treadmill. The big blades spinning push the air behind the plane and cause the palne to move forward. All the wheels do is make it so a plane isnt a piece of metal sitting on the ground. So once the engines are going, the plane is moving forward regardless of the ground under it. The treadmill spinning backwards would have no effect on the plane because the wheels rotate freely.

So you're agreeing with me, right?

I guess haha, I didn't read your posts. There was 200 on here so i just read a few and put what i thought.

Sorry, I'm lazy and am not going to read the 10+ pages before my post.

My answer: Of course the plane can take off...the treadmill has nothing to do with it because the plane isn't getting its speed from its wheels like a car, it obviously uses its props/jets. The only difference between this situation and a normal takeoff is that the wheels of the plane will be spinning twice as fast as normal, and assuming they don't fail under this increased stress, the plane will take off just fine.

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?

****** I HAVE THE ANSWER TO END ALL ANSWERS ******

This is all about semantics, and an unclear question.

Basically, BOTH SIDES ARE RIGHT!!!

Notice that the original riddle/question never specified what speed the treadmill would be matching. Does the treadmill match the speed of the plane moving RELATIVE TO THE TREADMILL or RELATIVE TO THE GROUND?

IT SIMPLY STATES IT WILL MATCH THE SPEED OF THE PLANE.

If the treadmill matches the speed of the plane relative to the treadmill, then NO, the plane WILL NOT take off.

If the treadmill matches the speed of the plane relative to the ground , then YES, the plane WILL take off.

Please attempt to disprove me. For you will be thwarted. And I love thwarting bitches.

Oh, and just to be clear about what I mean by "relative to the treadmill/ground" I'll give you guys a quick example.

Let's say that you're on this imaginary treadmill. If you start to run at 10mph and the treadmill moves at 10mph, then you are stationary to your surroundings. You're not going anywhere. Your speed RELATIVE TO THE TREADMILL is 10mph, but your speed RELATIVE TO THE GROUND is 0mph. Therefore, in this example the treadmill is matching your speed relative to itself.

Again, imagine yourself on this gigantic treadmill. You're running 10mph, but this time you're actually moving forward. You look at the gigantic treadmill interface and it says it is moving at 5mph. This is because your speed RELATIVE TO THE TREADMILL is 10mph, but your speed RELATIVE TO THE GROUND is 5mph. In this example the treadmill is matching your speed relative to the ground.

This is hillarious. We have 'aerospace' people who use logic that completely disproves their own conclusions and other people getting hot under the collar.

The only thing this riddle has proven is that some people are stupid full stop, the majority of others either have minds that can comprehend spatial/logical problems (masculine) and some have minds that cannot (femenine).

For the elimination of doubt, if you ignore the fact that a plane's wheel spinning at some rediculous speed would cause it to fail (we can do this as we are being asked to imagine there is a huge treadmill that can run to massive speeds) then the plane will fly.

Anybody using examples of runners, cars or any other vehicle that doesn't exert thrust should be discounted as either being stupid or simply missing the big fat point.

In my second post I did use running as an example.

However, if you switch a person running on the treadmill, with a plane moving on the treadmill, the explanation still stands.

I was just using "running" as an easy way for the obvious idiots on here to comprehend the idea of TWO different speeds. Being the speed relative to the treadmill and the speed relative to the ground.

Still wrong though as it is a red herring. Speed relative to the treadmill is not relevant. Air speed is the key and as the wheels are not generating the air speed, the engines acting on the still air are, then the plane will move through the air and this is the only relevant fact that will make the plane fly. Friction/rolling resistance will play a part but it is a minimal.

Ahmen!!!

tank wrote:

... the treadmill negates the forward movement.

How does the treadmill negate the forward movement? Its only point of contact is with the tyres. The wheels freewheel. GEDDIT? If you put the A/C on jacks you could rotate the wheels yourself. Backwards if you like. Does this mean the A/C will move backwards off the jacks?

THE ANSWER IS- IT WILL FLY

Everyone READ THIS AND PAY ATTENTION!!!!

Imagine your in a pool standing in water up to your chin on a treadmill. You are walking on the treadmill in the water. Your feet are pushing against the surface of the TM. NOW, you start to move your arms (jet engines) in a swimming motion while still on the treadmill. If you do this vigorously enough you WILL sart to move relative to the water and the ground, your feet(wheels)satrt to slide across the surface of the TM no matter how fast the TM is turning against you. You will be moving in a horizontal direction. Hypothetically if you keep accelerating (moving your arms-jets) fast enough you would gain enough speed to create enough pressure (air) under wings to get lift in the verticle direction.

You can think of water as denser air because it behaves the same way physically

That's the most simple and straight forward explanation. I would like to see somebody disprove that logic.

The riddle is not about symantics, double meaning or any other crap. It is designed to flummox those that are unable to think in a logical way.

If most of the people posting on here are American then I would say this thread should be the only evidence needed to prove the conspiracy theorist correct in their claims that the moon landings were a hoax!

Of course any views on any website have to be taken with a grain of salt, but that doesn't mean every dotcom site is rubbish. Items like these are not addressed on serious dot edu or dot gov sites because they are too trivial.

The AVweb is as good a site as any to get an explanation. Just like people come to Letsrun dot com for some training advice. Much of what appears on the Letsrun fora is drivel of the lowest order, but NOT ALL. The Letsrun website has a lot af factual info, too. The same follows for lots of other subjects, including Aviation.

It is. Since A/C do not apply thrust via the wheels the treadmill is irrelevant. You and other non-aviation types can't get your head around this. Admittedly, it's a bit counter-intuitive. As I said earlier, take it as read, until you can get your head around it. This problem was put out there to catch out clever, technical types (but non-aviation). Unless you have a background in Aviation I'd quit calling others who are "just some guy rambling on about his beliefs...". If you do know about physics then you should be able to grasp that the conveyor is irrelevant.

But a truck or a dog sled exerts the force against the ground. So a plane is different.

Of course he did. What training do you think pilots undergo? Obviously you haven't a clue. Check out the syllabus for the PPL; I'm sure it's somewhere on the web. I taught trainee pilots A/C electrical systems, and I can assure you they cover the whole gamut of subjects.

That's right. And don't bother with the expertise of an entire industry. Fresh out of HS and ready to contradict people who work at this stuff, for a living, every day of the week. That's your problem. Everything is 1st semester college physics. What would the Aviation industry know about aerodynamics, eh?

I'm changing my mind on this. The plane will fly.

The wheels are free moving, the engine propels the plane forward, and the wheels will just end up spining faster due to the treamill going in the opposite direction but will not affecting the forward progress of the plane.

Damn you are stupid!!

FREE BODY DIAGRAM BITCH!!

Please explain to me exactly what FORCE there is that is overcoming the THOUSANDS OF POUNDS of THRUST that the jet engines are producing.

Read my posts above and you will understand.

You have been thwarted, bitch.