Stupid physics question

[ECA]

Did the angry people miss my posts that bumped it about Mythbusters?

 

[Will]

No, thats why I haven't closed it yet. But people are still giving their personal opinions on a subject we did to death a long time ago now.

 

[Sharma]

Will's so angry these days

Angry scottish blokes = teh funney

 

[SawTooTH]

Oh for fucks sake. Can we not do this again? The answer is yes, because the plane is driven by gigantic jet engines on its wings, not by its wheels.

If anyone else posts up an answer, I'm locking the thread, because this fills me with teh rage!!!

Oh dear oh dear.

The conveyer is set up to cancel out the forward thrust of the engine. It won't lift off without forward motion. Jets can run their engines practically at full thrust with brakes on, you dont see them suddenly fly upwards, they need to be moving.
You need to pay more attention to the conditions of the question.

Its the wing btw that gives a plane lift, not the jet engine, else its a rocket

 

[nath]

lol.

The key point you mentioned there is "with the brakes on". The conveyor belt will not be capable of moving the plane backwards at any significant speed at all. The wheels will simply spin twice as fast when the engines speed up.

Though this has all been covered earlier in the thread

 

[SawTooTH]

lol.

The key point you mentioned there is "with the brakes on". The conveyor belt will not be capable of moving the plane backwards at any significant speed at all. The wheels will simply spin twice as fast when the engines speed up.

Though this has all been covered earlier in the thread

But you forget gravity

Okay gravity is keeping the plane on the conveyer the thrust is increasing on the engine but the plane doesn't move forward as the conveyer is in balance with the thrust. Yes the wheels spin faster but the plane isnt moving relative to the ground. So explain how the air is moving over the wings to generate lift. Your explanation only works when the conveyer fails to keep up with the thrust.

The whole things preposterous and I wouldnt want to be anywhere near a conveyer that could do that still...

Have you ever walked the wrong way on one of those conveyers in airports...you get nowhere fast. Okay now run and the conveyer matches your speed. you still aren't going anywhere are you? Okay attach a wing to your arms and repeat. You now are superman and can run faster than a speeding train...but the conveyer and gravity keep you on the ground as no air is moving over your wings...wheres the lift?

 

[TdC]

but imagine you're on rollerskates with a propeller strapped to your back. the spinning wheels compensate.

trust me, I answered no in the poll. since then I have learnt the error of my ways!

 

[Deebs]

Yes, your plane is really a helicopter with wheels and wings strapped to it!

 

[nath]

You're missing the point sawtooth. No one is suggesting that a plane takes off when it's stationary (relative to the ground). People are saying that regardless of the conveyor belt, it's going to move forward. The fact being that the forward thrust is generated by something COMPLETELY independent of the wheels hence the conveyor belt is going to be completely ineffectual in keeping the plane stationary.

 

[Tom]

Oh dear Sawtooth.

Oh dear.

 

[old.user4556]

I want to summon Bodhi and Wazz to this thread to unleash a torrent of the worst verbal abuse ever witnessed onto you, Sawtooth.

 

[Tom]

BTW this thread should be in that 'threads before you die' post.

 

[Bodhi]

lol.

The key point you mentioned there is "with the brakes on". The conveyor belt will not be capable of moving the plane backwards at any significant speed at all. The wheels will simply spin twice as fast when the engines speed up.

Though this has all been covered earlier in the thread

But you forget gravity

Okay gravity is keeping the plane on the conveyer the thrust is increasing on the engine but the plane doesn't move forward as the conveyer is in balance with the thrust. Yes the wheels spin faster but the plane isnt moving relative to the ground. So explain how the air is moving over the wings to generate lift. Your explanation only works when the conveyer fails to keep up with the thrust.

The whole things preposterous and I wouldnt want to be anywhere near a conveyer that could do that still...

Have you ever walked the wrong way on one of those conveyers in airports...you get nowhere fast. Okay now run and the conveyer matches your speed. you still aren't going anywhere are you? Okay attach a wing to your arms and repeat. You now are superman and can run faster than a speeding train...but the conveyer and gravity keep you on the ground as no air is moving over your wings...wheres the lift?

You're missing one key point. The movement of the plane is not caused by the wheels. You're thinking of it as a car, where of course the motion of the wheels will get counterbalanced by the conveyor belt, hence car will not move. However a plane has dirty great big jet engines which act on the plane ITSELF, not the wheels. The wheels move as a result of the motion of the plane, not the other way round. So, as long as the plane isn't being physically held back (like if they try full throttle with the brakes on), the jet forces will still be acting on the plane, moving it up the runway, fast enough to take off eventually. The wheels will just be moving at twice the speed.

 

[Chilly]

~inhales~
AAAAAAAAAAAAAAAAARRRRRRRRRRRRRRRRRFGGGGGGGGGGGGGGGGGGGGGGGGGHHHHHH!

fuck sake

 

[Wij]

Noooo - not again !!!!!!!!!!1

 

[Scouse]

Surely everyone who thought the plane wouldn't take off has discovered the error of their ways by now???

 

[Wij]

Ooogh - says you

 

[Garaen]

I've just wasted an hour of my life reading this entire thread lol. I understand that the major issue is that the wheels of the plane don't work the same as a car; that the thrust of the plane comes from the engines yet there is one thing i can't get through my head. If the plane's engines are working at their maximum capacity surely the forward motion is transfered to the wheels until the plane takes off, which can be negated by the conveyer belt?

 

[Will]

The engine on a car (or a bike) accelerates the wheels. If the conveyor belt turns, the wheels are still accelerated, but the motion of the conveyor belt against them means the body of the car does not move.

The engines on a plane accelerate the plane itself. The conveyor belt would make the wheels spin faster, but the body of the plane is still being driven directly by the jet engine, and so will move forwards.

Does that explain it better?

 

[Chilly]

fuck the wheels, fuck the plane and fuck mythbusters!

 

[dysfunction]

The engine on a car (or a bike) accelerates the wheels. If the conveyor belt turns, the wheels are still accelerated, but the motion of the conveyor belt against them means the body of the car does not move.

The engines on a plane accelerate the plane itself. The conveyor belt would make the wheels spin faster, but the body of the plane is still being driven directly by the jet engine, and so will move forwards.

Does that explain it better?

So what you are saying is if you switch the plane's engines off (and the brakes are off) the plane will remain in the exact same spot (relative to the ground) on the conveyor belt...it won't get pushed backwards?

 

[Chilly]

of course it will you idiot.

 

[Clown]

Idiot.

 

[Will]

Of course I wasn't saying that. Though for a set of perfect wheels, with no friction, that would be the case*.

I can't believe I am trying to justify the correct answer all over again, 18 months later, one person at a time. This is why I was going to close the thread.

*If you are having trouble understanding why the answer is yes, please don't think about the problem from a theoretical mechanics point of view. You'll just hurt your brain.

 

[TdC]

Will's so angry lately

 

[Insane]

Will's so angry lately

He just needs to get laid.

someone send trem round

 

[Will]

He just needs to get laid.

someone send trem round

I'll stick with my other half.

 

[Jupitus]

*fap*


(someone was gonna do it! )

 

[TdC]

yeah, but you did it first! dirty bugger o0

 

[Will]

That make up and effects took me 3 hours. I'm glad someone fapped.