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Which of the following statements are wrong?

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LAN_403

HV Enthusiast

Mon Jul 24 2006, 12:04AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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A. Oceans, lakes, and bodies of water are blue because they reflect the sky.

B. Electrons flow through wire at nearly the speed of light.

C. Aircraft fly because the upper surface of the wing is longer than the lower surface.

Quantum Singularity

Mon Jul 24 2006, 12:24AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Well, i suppose I'll take a stab...

I would have to guess that C is the only correct one. A, the ocean reflects blueish light, that just happens to be the same color as the sky - not from the sky. B, it seems as though I read somewhere that an individual electron travels much slower than the speed of light, but if one electron enters one end of the wire another will be pushed out giving the effect that the electron traveled at nearly the speed of light when its actually a different electron and the original one is still yet to come out. C, I beleive is correct since my understanding of a lifting wing is that the longer area on top of a wing makes the air speed up creating a low pressure where as under the wing the air is slower created a high pressure, with the pressure difference creating lift... not 100% sure though...

Liam

Mon Jul 24 2006, 12:26AM

Registered Member #113 Joined: Fri Feb 10 2006, 01:40AM
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A is wrong because heavy water isn't blue.

B is wrong for obvious reasons.

C. Not necessarily, there are symmetrical wings that are identical on the upper and lower camber. Also, little consideration is given to the upper camber vs. lower camber in most paper airplanes, yet they still manage to fly. Reaction lift could keep an aircraft aloft all by itself, although it would be rather slow and would need quite a bit of power.

rev

Mon Jul 24 2006, 01:08AM

Registered Member #112 Joined: Fri Feb 10 2006, 01:19AM
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all three are both right and wrong based on the way they were presented.

a) will reflect light but will not iluminate corispondingly. it's a mater of what is desolved in it. there is alot of blue from our sky so if it is luminesant to blue then it will reflect alot of blue.

b) "nearly" the speed of light is a loose claim. i can run at nearly the speed of a hungry aligator if compaired to a unwary turtle. the only way to guage this would be to run tests in a vacume. i know nothing of test runs like this but i will say this. it's a matter of the wave lenghth. distance covered over time.

c) they fly becuase there is a force be it pull from a motor or gravity and thermals. i can make a aeroplane (and have) that is a flat plane with no more than a lower hull and calculated CG. the next step up would be a SPAD made from pizza boxes or what ever other corigated material you can get.(non metal preferably)

and that was rev's "no highschool education but played with things enough to understand them" responce..

i'm thrilled by your question. i can't wait to see where this gose. maybe i can get some replacements for my very simple and blunt explainations. maybe even more stuff to google for.

AndrewM

Mon Jul 24 2006, 02:50AM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

I don't think you hit it quite rev.

a) Pure water, I believe, is still blue without dissolved solids. Its for the same reason the sky is blue, increased scattering efficiency in the blue wavelengths.

b) Way off. Electron drift velocity is usually near walking speed.

c) The 'how do airplanes fly' question is always answered in one of two ways 1) wrong, or 2) incomplete. Some would argue that plane fly because of reduced pressure over the top wing. Some would say that the increased fluid velocity over the wing makes them fly. Still others (as in this case) would insist that its the Kutta condition that is responsible. You can pretty much pick which one you like to be the 'correct' one as they are all related, but all incomplete. I would say that the way its presented here is the least correct, as certain wing shapes with longer upper surfaces can indeed NOT accelerate the flow and produce no lift. The 'increased' velocity case is better, although it eschews specifics about flow separation, compressibility, etc. I like the reduced pressure on the upper surface as it comes pretty close as is generally the most correct. It too, however, doesn't mention the myriad other forces of lift found in wings.....

EEYORE

Mon Jul 24 2006, 03:21AM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

A is wrong...The rest are correct.

Matt

Tom540

Mon Jul 24 2006, 03:39AM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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A. water is blue because it absorbs high amounts of red according to an article I read. B. Radio waves travel at the speed of light but electron flow in a circuit or wire is much slower, so b is wrong. C is wrong hehe The wing deflects the air downwards. You can make a glider with a styrofoam plate and a penny and the wings will have the exact same size top and bottom and it will still fly.

AndrewM

Mon Jul 24 2006, 04:07AM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
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Beleive it or not Tom, that is not the primary lift producer, even on flat airfoils. Flat airfoils still produce pressure gradients in linear proprtion to their angle of attack.

Simon

Mon Jul 24 2006, 04:57AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

They are all a bit funny.

A is yes and no. If I'm standing on the shore looking at the water, a lot of the colour I see is just reflected from the sky. If I'm on a row boat looking down into the water, reflected light has very little to do with anything.

As Andrew said, the drift velocity of electrons in a wire is famously described as "near walking speed" in just about any physics textbook or lecture. Electrical effects in the wire propagate according to the speed of light in the wire, which is nearly the speed of light in a vacuum.

C is the typical explanation given in school textbooks but, again, as Andrew said it's a lot more complicated than that. There's more than one way of looking at it, too. Having just done a whole lot of aeronautics related stuff, he can explain it better than me.

Here's one for EVR to decide. Right or wrong:

The creator of this thread has plenty of time on his hands right now.

Bored Chemist

Mon Jul 24 2006, 04:58AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

answer "d" None of the above.

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