Science questions not worth a thread I: I'm a moron!

IdiotsOpposite said:

Well, Newton's Laws are correct, or at least a very good approximation. If they were completely wrong, we wouldn't teach them, after all!

However, on very large or very small scales (think galaxies or atoms), Newton's laws begin to be a lot worse. This is where we get the current theories of relativity and quantum physics.

As to your last paragraph, I think you're looking for the Theory of Everything, and while it doesn't exist yet, we're trying. We're trying hard.

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yeah but still Newton's theory have been replaced by General Relativity. i was thinking more about fluid mecanics or any theory that can explain everything in its field being chemistry or biology.

and not because they teach them it is correct. in high school they never talked about quantum. all we got was Bohr's atom...yet that theory is wrong but like newton's theory easier...

NKVD said:

yeah but still Newton's theory have been replaced by General Relativity. i was thinking more about fluid mecanics or any theory that can explain everything in its field being chemistry or biology.

and not because they teach them it is correct. in high school they never talked about quantum. all we got was Bohr's atom...yet that theory is wrong but like newton's theory easier...

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It's not so much that they're wrong, but that they're not as accurate as they could be. They're simplified versions that are useful provided you use them in the right context. From memory, if you take relativity, and simplify the equations to ignore the tiny, pretty much irrelevant bits for a particular model, like a model that deals in human scale speeds and distances, then you get Newton's stuff anyway. Of course, if you ignore those same bits for stuff on a different scale, then you just get the wrong answer. Which is why Newton's laws don't work for those things.

Strictly speaking, Newton's laws are wrong, but that doesn't mean they're not useful. Or to quote a physics professor (on a completely different matter): "I know it's wrong, but I can explain it anyway else"

NKVD said:

Questions after reading a book on Newton.

Just like Newton's law which proved as a verified theory for a long time. Is there anything Newton's law couldnt explain or predict ?

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Yes, for example the orbit of the planet Mercury around the sun or the sharp absorption lines of atoms. Both problems were known in the 19th century and could not be explained with Newton's laws. At that time people thought that physics was more or less solved, with just a few loose ends remaining. Little did they know what was hidden behind these loose ends.

Which laws proved true or was verified in the past (meaning it could explain or predicts everything observed) but was proven wrong years later.

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One prominent example would be the theory of light as an electromagnetic wave. Until the photo effect was thoroughly investigated it could explain all the properties of light. By now we know that there is quite a bit more to light than just Maxwell's equations.

But of course there are countless other examples of how a highly successful theory turned out to be not the whole story.

I know some of you will answer every theory. But is there any complete theory on earth ? i think yes.. but we know most of todays theories are not complete.

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There is no way to prove that any theory is complete as that would involve test it against all imaginable and unimaginable situations. The closest you can ever get is that there is no observation that contradicts the theory. But there might always be the one stupid special case out there that contradicts the theory.

The most complete theories are certainly the fundamental ones. Quantum electrodynamics for example is amazingly accurate. The theories more specific to a field are usually not as complete as they're only valid inside their (sometimes very strict) limits. Fluid dynamics is a field where there is no remotely complete theory at all, as fluids are extremely difficult to describe.

uppi said:

Yes, for example the orbit of the planet Mercury around the sun or the sharp absorption lines of atoms. Both problems were known in the 19th century and could not be explained with Newton's laws. At that time people thought that physics was more or less solved, with just a few loose ends remaining. Little did they know what was hidden behind these loose ends.

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i remember also reading some physicists thought physics was almost complete after Bohr's model and maxwell equations.

I also remember reading that the patent office director in USA said in near the beginning of the 1900's that by 30 years there would be anything new to invent since all would be invented...

Bill Gates also said he couldn't see any reason to have more than 640K memory in computers.

ParadigmShifter said:

Bill Gates also said he couldn't see any reason to have more than 640K memory in computers.

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Because Pr0n and video cards hadn't advanced that far at the time!

I won't go into Clive Sinclair saying a ZX81 could run the systems in a nuclear power station.

How do I calculate the minimum orbital distance of a planet orbiting both stars of a close binary system?

Dunno.

3 body systems are chaotic though, so do a simulation.

Its not really a 3 body system though, as to an excellent approximation the motion of the stars is independent of the planet. So you can solve the motion of the stars using standard elliptical geometry (this is quite easy as a two body system can be reduced to a 1 body system using reduced mass and relative co-ordinates). I'm not sure if you can then solve the motion of the planet analytically once you have this 'fixed' solution. Probably not, but it should then be trivial to write a program that calculates it numerically.

Sounds like a good assignment actually, might try it later as some mechanics revision.

That went waaaaaay over my head.

I'm just looking for something I can put into my computer's calculator (or wolfram alpha), like x times y = z, where x = the orbital distance between the two stars, either in AU or KM, y = whatever multiplier i need to use, and z = the minimum distance from the two suns a planet can orbit before getting unstable, again in AU or KM.

What I need is that magic multiplier number that is y.

The problem is that physicists have been searching for such a thing for about 300 years and there is still no comprehensive answer.


With some advanced math (perturbation theory might work) you could probably get a good approximation, but even then it won't be that easy. For example I would expect the solution to heavily depend on the relative masses of the stars and the planet.

Can someone help me with thermal conductivity? I want to find out what temperature the inside of a glass would have if the outside is wrapped with about 90ºC. It's not super important for my report, as it's about something completely different, but it would be cool to know what temperature each side of a glass cylinder has.

The left side of the cylinder is wrapped with a floorcloth with boiled water poured over, we can say the water is on 90ºC. The other side is wrapped with a floorcloth with water on maybe 3ºC.

The cylinder is made out of glass, it contains about 1500cm^3 air, it's 30 cm long. Both ends has a rubber cork reducing the air leaks.

Please? I'm not haven't done this part in physics yet, but it would be cool telling the teacher what temperature it has.

Is it something to do with specific heat capacity?

http://en.wikipedia.org/wiki/Heat_capacity

I do not know. I just want to find out the most possible temperatures inside the cylinder at each end.

scientific solution:
I can't remember my lesson on thermodynamics (too long ago, and never used) but IIRC you also need heat transfer coefficient as there is probably some kind of heat-flux between the cold and hot end (or is one side heated permanently and the other cooled?).
The system itself is not so simple as there are two interfaces (watered floorcloth)<->(glas), (glas)<->(gas) if you neglect the (water)<->(floorcloth) and the (glas)<->(rubber) and the (rubber)<->(gas) interfaces. Also one big question remains: is there a direct hot<->cold interface or are the cold and hot clothes just connected by the cylinder (and the surrounding air)

engineering solution:
put a thermometer into the cylinder

The floorclothes was probably something like 85 degrees <-> 4 degrees.

In principle you need to define your boundary conditions and solve the Heat_equation. I think this would have to be done numerically and you would need to know the thermal diffusivity of the materials involved.

If that's to complicated, you could think about how to simplify the problem until you can solve it. For example by assuming that the temperature of the floorcloths stays constant or that the heat transport of the air inside the cylinder is negligible. You have to condense the problem to one that is easily solvable, but still depicts the situation accurately enough.

Meh whatever then.

How do you calculate the length of a parabola?