Letrun.com was right...the plane DID take off!

I don't get it. The plane was moving forward, where is the treadmill part of this?

It looks to me like the "treadmill part" is a long tarp or something that is being pulled by a car/truck in the opposite direction that the plane is moving.

Ok, now I understand that part. Is it me, or is the plane still moving forward?

I do think the plane described in the riddle would talk off.

That said, the show sucked, the experiment sucked and those two guys are fruits.

That moving tarp proved nothing. Yes it was moving, but at what speed?

Say the tarp was moving at 15 mph and the plane was moving at 40 mph?

That's the point--the plane is still able to move forward at normal speed even though the the treadmill is going backwards because the wheels freely rotate and the thrust comes from pushing off the air, not the ground. No one ever said that the plane would take off if it wasn't moving relative to the air (ok, maybe some people said that, but they were idiots). They just said that the plane would still be able to move forward at basically normal speed and take off because there is very little friction in the wheels.

You people will never get it - others don't even try to explain.All I can say is think about it REAL hard and let your mind be open

? wrote:

Ok, now I understand that part. Is it me, or is the plane still moving forward?

I am not trying to be stupid, or such. I didn't follow the other threads on this.

Yes, that all seem pretty basic. Then what is the point of doing it?

here we go again wrote:

That's the point--the plane is still able to move forward at normal speed even though the the treadmill is going backwards because the wheels freely rotate and the thrust comes from pushing off the air, not the ground.

Wait a second, what you are saying is that the plane is already flying? Then how does it obtain enough speed to take off?

Somehow I missed the other threads until this week when a guy emailed me all excited about the plane thing being on the A&E show.

I then was reading the old thread which was from 2 or 3 years ago. Did some letsrun viewer submit the question to the show and get it on the air? Or was it already going to air and some letsrun guy started talking about it.

If you have a decent grasp on the laws of physics, this is a no brainer. My father-in-law is an engineer and I figured he had a pretty strong background in physics and mathematics. So I proposed the plane-treadmill riddle to him. He just looked at me for a second and said, "Well it doesn't matter how fast the treadmill is running. The wheels spin freely. The plane will move forward indepedent of the treadmill speed." Then he just sort of laughed and stopped talking about it, as if to say "What a dumb question. Of course the plane would take off."

Oops, I get it. Nevermind.

I honestly don't know, wejo. I think I stumbled upon one of those old threads long after they'd been started. Perhaps this "treadmill question" is an enduring urban legend or myth independent of letsrun. It does seem to crop up on other message boards about science, math, etc.

i kinda like running wrote:

If you have a decent grasp on the laws of physics, this is a no brainer. My father-in-law is an engineer and I figured he had a pretty strong background in physics and mathematics. So I proposed the plane-treadmill riddle to him. He just looked at me for a second and said, "Well it doesn't matter how fast the treadmill is running. The wheels spin freely. The plane will move forward indepedent of the treadmill speed." Then he just sort of laughed and stopped talking about it, as if to say "What a dumb question. Of course the plane would take off."

And how many posters said the exact same thing in previous threads? Some people are just too dumb to get it.

boredman wrote:

Some people are just too dumb to get it.

Very true. On the other hand, other people made it far enough in physics that they progressed past the idealized toy problems that you solve in high school or undergraduate physics. In the real world, wheels aren't frictionless, and the ability of the plane to take off will depend crucially on the specific characteristics of the surface (and length) of the treadmill. There's no general answer either way.

There is also ambiguity in the way the question was posed (in some places), since it didn't define whether the treadmill would match the wheel speed (the ground speed, effectively) or the air speed on the plane. Those are two very different scenarios.

In short: yes, there are plenty of dumb people around here, but if you can't fathom how anyone came up with a different answer, you're one of them.

In the original problem the treadmill only matches the planes speed, nothing more. There is virtually no ambiguity in the problems original wording. The length of the treadmill would not have been a factor anyway.

In the real world you mention I'd bet giant treadmills have a far greater failure rate than wheel bearings. I myself am an industrial designer and manufacturing consultant, this problem is far from an "idealized toy problem". It is however, a fairly straight forward problem with a simple answer.

I saw long ago how and why people were not getting it, some came around, some didn't. If you didn't get it, then you didn't get it. Don't feel too bad, you weren't the only one.

boredman wrote:

In the original problem the treadmill only matches the planes speed, nothing more. There is virtually no ambiguity in the problems original wording. The length of the treadmill would not have been a factor anyway.

In the real world you mention I'd bet giant treadmills have a far greater failure rate than wheel bearings. I myself am an industrial designer and manufacturing consultant, this problem is far from an "idealized toy problem". It is however, a fairly straight forward problem with a simple answer.

I saw long ago how and why people were not getting it, some came around, some didn't. If you didn't get it, then you didn't get it. Don't feel too bad, you weren't the only one.

Well, you certainly managed to misunderstand everything I wrote. Sadly, I doubt that typing it again will improve your chances of understanding, but let me at least point out that "matching the plane's speed" could conceivably refer to either ground speed or air speed, and that failure of wheel bearings has nothing remotely to do with the wheel friction I'm referring. Yes, wheels have friction, even when the bearings are working perfectly -- and that's why the length of the treadmill matters, because distance it takes the plane to reach take-off velocity will depend crucially on the how much of an affect friction has on the plane's initial acceleration.

However, feel free to ignore all of that, as you're clearly one of those people who is incapable of seeing more than one side of an argument.

Exactly where did I argue that wheels have no friction?

If the treadmill was shorter, the plane would take off sooner than if the treadmill were longer. So what. The original problem only asks if the plane will take off. The plane takes off regardless of treadmill length.

The only condition that must be met in this instance is that the planes wheels must be able to spin approximately twice the speed necessary to take off without the treadmill.

Dude, you're pathetic. This isn't an argument, the problem was solved.

hold the phone wrote:

However, feel free to ignore all of that, as you're clearly one of those people who is incapable of seeing more than one side of an argument.