MythBusters tackles "plane on a conveyor belt problem"

[kernatch]

I thought the focus of the question was on how flight works and not on how ground force affects planes.

Yep, and you were wrong to do so; the entire point of the question was to trick some people into thinking exactly that. Do you think you can deal with the fact you were wrong yet?

[Fred Derf Veteran]

What I'm saying is that I thought the question was saying "the plane is stationary, what happens?" and not "will the plane BE stationary?". I thought the focus of the question was on how flight works and not on how ground force affects planes.

Which is why other people, ones who completely understand how a plane works, did not accept that the plane would remain stationary. They concluded that the plane would move forward and thus that the plane would take off. You, on the other hand, got caught in the trap for lay people.

[Kushan]

So really, the focus of the question was to see if people got caught or not and has nothing to do with planes?

If even pilots get the answer wrong, I think it proves that the question is poorly worded, a trick question even.

[+StevoFC MVC]

The fact the pilot kept saying he thought the plane would "sit there like a brick" made me realize that the guy had no idea what he was even talking about. It was, and still is, so obvious that the plane would still take off. Anyone who knows anything about how planes work could tell you that.

It doesn't matter how the damn question was worded. It flies...simple as that.

[Menge]

So really, the focus of the question was to see if people got caught or not and has nothing to do with planes?

If even pilots get the answer wrong, I think it proves that the question is poorly worded, a trick question even.

i don't think the question was badly worded nor that it's a trick question. nowhere in the question does it say that the plane will be stationary:

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

the answer is pretty obvious to anyone who:

1) knows how a plane moves

2) knows the three laws of newton

[BigDaddy5]

the answer is pretty obvious to anyone who:

1) knows how a plane moves

2) knows the three laws of newton

Eh, not really. Newtons laws aren't the reason the plane flies. I mean they are, but not completely. It's hydrostatic equilibrium and Bernoulli's principles that really make the plane fly. But that's splitting hairs, really. Bottom line is the plane took off, just as it should have.

There are a ton of other physical reasons the plane flies which I really could dive into in great length.

[kernatch]

http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html

[beardedwonder]

Yes, they knew it would go forward, but that never even factored into it for me and many others. Read what I'm saying, I interpreted the conveyor to just be a way of keeping the plane stationary, nothing more. It may as well have said "an anti-gravity field is placed upon the plane to prevent it moving forward" for all I cared.

How can you keep a plane 'stationary' with a conveyor belt? In essence the conveyor belt is a red herring, which i find funny! It was obviously going to take-off, how did you imagine it was going to take-off if it was stationary (the engines weren't running)?!

Edited January 31, 2008 by beardedwonder

[Menge]

Eh, not really. Newtons laws aren't the reason the plane flies. I mean they are, but not completely. It's hydrostatic equilibrium and Bernoulli's principles that really make the plane fly. But that's splitting hairs, really. Bottom line is the plane took off, just as it should have.

There are a ton of other physical reasons the plane flies which I really could dive into in great length.

but it's the proper use of newton's laws that proves that the plane actually moves in THIS case. i'm not saying you're wrong about bernoulli's principles. just saying that the bernoulli's principles weren't in question in this case. almost everyone in the thread applied them correctly. what most people were doing was actually applying newton's laws wrongly here. that's why i only mentioned those.

anyway... it's all over: the plane takes off and i feel sorry for the pilot for saying that it wouldn't :)

[Fred Derf Veteran]

They may have screened 1000 pilots to get one who thought that it would stay stationary.

[BigDaddy5]

but it's the proper use of newton's laws that proves that the plane actually moves in THIS case. i'm not saying you're wrong about bernoulli's principles. just saying that the bernoulli's principles weren't in question in this case. almost everyone in the thread applied them correctly. what most people were doing was actually applying newton's laws wrongly here. that's why i only mentioned those.

Well, where I was going with that was more along the lines of why the plane moves forward to begin with. It's a combination of Newton and Bernoulii. The rotar spinning creates an air pressure difference (it doesn't push air over the wings to make lift) in front of the air plane, which causes the plane to be pushed/pulled forward by that difference. That's Bernoulli. There is a force pushing against the air, so there has to be an equal and opposite reaction against that. That reaction is the plane moving. That's Newton. Hence the combination of laws.

Newton's laws take care of the conveyor; the negative motion of the conveyor is transfered to rotational motion through the wheels since, so all motion is conserved there. Since the wheels spin independently of the plane, that component is taken care of.

But if the plane stands still, that means the force the propeller creates has no opposite force acting on it, so there is no conservation of forces...which would violate the laws of physics.

Like I said, I could go on for a long while about why this worked/works, but you already get the idea so I'll shut up.

[curme]

Mythbusters, airplane on a conveyor belt, it would make a great t-shirt! "Hell yeah! It took off!" or "I don't care, what they say, it won't fly!"

Somebody should make a thread with t-shirt designs! I have an idea for one, but I'm on the midshift now and won't have time to work on it in a while.

I'm sure threadless.com and the net will be flooded with them in no time.

[Spyder Veteran]

So really, the focus of the question was to see if people got caught or not and has nothing to do with planes?

If even pilots get the answer wrong, I think it proves that the question is poorly worded, a trick question even.

Of course its a trick question. People who think that the ground makes any difference in a plane/jet's momentum will get stumped by the conveyor belt. The conveyor could be going even faster in the opposite direction than the plane and it would still take off. The ground/conveyor means nothing to a plane.

[The_Decryptor Veteran]

Mythbusters, airplane on a conveyor belt, it would make a great t-shirt! "Hell yeah! It took off!" or "I don't care, what they say, it won't fly!"

Somebody should make a thread with t-shirt designs! I have an idea for one, but I'm on the midshift now and won't have time to work on it in a while.

I'm sure threadless.com and the net will be flooded with them in no time.

http://www.cafepress.com/planetakesoff

[Echilon]

I thought it would remain stationary, until I realised what they were saying about the driving force being transferred through the air and not through the wheels.

Made a lot of sense.

[Nicholas-c Veteran]

I thought it would remain stationary, until I realised what they were saying about the driving force being transferred through the air and not through the wheels.

Made a lot of sense.

same :p