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Post by nomuse on Apr 10, 2006 5:23:58 GMT -4
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Post by gwiz on Apr 10, 2006 5:34:30 GMT -4
It's the sheer confidence they have in their answers that's so impressive, flat wrong but sure they're right.
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Post by PhantomWolf on Apr 10, 2006 7:45:57 GMT -4
I started to read it and then stopped when I realised they were still arguing about it -332- pages later
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Post by echnaton on Apr 10, 2006 9:29:49 GMT -4
The latest post contains this gem.
“Assuming there was no prop or jet engine, am I right in thinking that it (an airplane) would not take off?”
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Post by PhantomWolf on Apr 10, 2006 10:13:06 GMT -4
I'm still getting over the people that think that a Jet engine "pushes against the air." No, a Jet engine is a special case of Rocket engine where the propellent is gathered from the surroundings and compressed, rather than being contained in the rocket itselt. Thus it's mechanism is the same as a rocket's, it's Conservation of Momentum. i.e. You fire a blast of highly compessed air out the back as thrust, and the jet moves forward. So far I love this comment the best. Even when they get it right, they get it wrong!!!!!! |
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Post by nomuse on Apr 10, 2006 16:28:26 GMT -4
It's an instructive argument. The original question was unclear on whether the plane was held stationary. If you take the question to mean, exactly, "the treadmill moves backwards as fast as the plane moves forwards (both in reference to the ground), you get after an interval a plane making 200 knots west, a treadmill making 200 knots east, wheels spinning at 400 knots equivalent, and the plane lifts off without trouble.
What happens in the thread is several people realize how silly this is and "help" the original question by assuming zero ground speed. The plane accelerates forwards, the treadmill then races backwards fast enough so the friction drag on the wheels pulls the plane backwards. That would be some speedy treadmill, I think. After all, ski planes take off. DC-3 could take off dragging a wooden-hulled glider behind them. As one person pointed out, this is probably an ineffective way to apply the proper acceleration to the plane until the bearings and tires smoke and break down. (Hrm. Yah, and then there's that plane recently that landed with the nose gear sideways. No problems, and the wheel didn't even break off.)
But in any case....the rest of the three hundred pages is people arguing from one of these two sets of assumptions and Failing To Realize the other person is using the other set. It is three hundred pages of posters assuming that every other poster to the thread is a drooling idiot who missed the basic physics of it....because they themselves are still stuck back on a post #1 understanding.
No. I didn't read the whole thing. I don't think anything human could.
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Post by jaydeehess on Apr 10, 2006 18:46:59 GMT -4
I was originally fooled and thought the treadmill was keeping the plane stationary.
Yes the plane flies, the wheels simply freewheel twice as fast as if the treadmill were not in motion(ie a runway)
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reynoldbot
Jupiter
A paper-white mask of evil.
Posts: 790
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Post by reynoldbot on Apr 13, 2006 11:51:02 GMT -4
From the first post on that thread:
his conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).
I was under the impression that the plane was not moving. It sounds pretty clear to me by the above statement. If the plane could still move, what would be the point of asking the question?
I certainly don't feel like reading 300 pages + of "nuh uh! It could totally take off dude!" and "Pshaw! Your (sic) and idiot! It would never take off!"
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Post by nomuse on Apr 13, 2006 15:40:48 GMT -4
You hit that nail on the head, reynold.
The _question_ is absurd. Treadmill, smeadmill. It doesn't matter if the plane is sitting on a magic carpet, as long as it is not materially prevented from moving forward under the impetus of its engines.
I think the following posts are either too stupid to figure that out, or too smart; they _know_ the treadmill doesn't do squat so they alter the question to make it more interesting.
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Post by phunk on Apr 17, 2006 16:33:10 GMT -4
Unfortunately there's no way to make it more interesting.
Either the treadmill matches the speed of the plane with relation to the ground, and the plane can move, or the treadmill magically moves fast enough for the friction in the wheels to hold the plane back, and the wheels basically instantly explode as all of the engine thrust is converted into heat in the bearings and rotational energy in the wheels.
Damn did I just sum up both sides of a 300+ page argument in 1 sentence?
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Post by Fnord Fred on Apr 17, 2006 16:44:27 GMT -4
Unfortunately there's no way to make it more interesting. Either the treadmill matches the speed of the plane with relation to the ground, and the plane can move, or the treadmill magically moves fast enough for the friction in the wheels to hold the plane back, and the wheels basically instantly explode as all of the engine thrust is converted into heat in the bearings and rotational energy in the wheels. Damn did I just sum up both sides of a 300+ page argument in 1 sentence? I think you did. We had a similar discussion in one of my first college classes, where a bicyclist was riding in a 10 MPH wind at 15 MPH (numbers could be different but you get the idea). I tried pointing out that you can't just subtract the wind speed from the total speed because there's more traction along the ground than there is in the air and you have to consider a variety of factors such as aerodynamics, air pressure, etc. You COULD have a wind that was blowing HIM back at 10 MPH, but the speed of the wind itself would be so ridiculously high that you wouldn't want to be riding out in it in the first place. Sadly, intermediate algebra students have little respect for physics. I tried pointing out that if I walk out into a 20 MPH windstorm (a common occurence in the desert), I won't get blown the other way at 15 MPH. They insisted that somehow it was different because 'hes on wheels.' |
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