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MythBusters tackles "plane on a conveyor belt problem"


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#331 BigDaddy5

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Posted 31 January 2008 - 16:17

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.


#332 kernatch

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Posted 31 January 2008 - 16:45

http://www.grc.nasa....ne/bernnew.html

#333 beardedwonder

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Posted 31 January 2008 - 18:24

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 by beardedwonder, 31 January 2008 - 18:41.


#334 Menge

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Posted 31 January 2008 - 18:33

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 :)

#335 vetFred Derf

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Posted 31 January 2008 - 21:41

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

#336 BigDaddy5

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Posted 01 February 2008 - 03:07

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.

#337 curme

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Posted 01 February 2008 - 13:33

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.

#338 vetSpyder

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Posted 01 February 2008 - 14:44

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.

#339 OP The_Decryptor

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Posted 01 February 2008 - 14:48

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

#340 Echilon

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Posted 07 February 2008 - 20:57

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. Posted Image

#341 vetNicholas-c

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Posted 08 February 2008 - 00:07

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. Posted Image


same :p