Science Quiz

[Kinniken]

TLC wins. Four minutes... The next one will be harder.

Amazing feat BTW when you think he managed that in the third century BC only by studying a few shadows, while most of the world continued to think the earth was flat for centuries after that...

 

[col]

It was the slave that had to pace out the distance from the needle at Alexandria to the well at ? I feel sorry for. About 60 miles if my memory serves me right.

 

[The Last Conformist]

This might be a bit harder:

Who first demonstrated that the speed of light is finite, and how?

 

[betazed]

I do not think it was any one person who can be contributed to that. Olaf Roemer, Christian Huygens, Bradley all contributed to the experiments and notions that finally proved that light has a finite speed.

<edit>: I forgot the how part. Both Bradley and Huygens proposed and showed that if the speed of light was finite then the point of colinearity of the earth moon and sun during an eclipse would be lost. This method was actually used earlier by Olaf Roemor with Jupiter and its moons.

 

[The Last Conformist]

Ole Rømer is usually quoted as having first rigorously demonstrated it (in the books I've seen, at least). He showed that the exact times of the occultations of the moons of Jupiter varied in time proportionally to the distance between the Earth and Jupiter.

So much for a harder question ...

You go:

 

[Kinniken]

Originally posted by col
It was the slave that had to pace out the distance from the needle at Alexandria to the well at ? I feel sorry for. About 60 miles if my memory serves me right.

The well was in Syene (Aswan today), which was 800 km from Alexandria, not a mere 90. I have heard however that the distance between the two was known to the Greeks before he used it for that purpose. It is even possible that he never went to Syene himself but relied on the testimony of someone else.

 

[betazed]

Ok. So let's have a really hard one.

(Hoping Col can shed some light here! )

Why do like charges repel and opposite charges attract?

 

[nonconformist]

Because the electrons won't interlock with each other and keep a stable connection?

 

[betazed]

nope. nothing like that.

It is a pretty deep question and I am hoping someone will give a nice clean answer.

 

[The Last Conformist]

It's not the sort of thing I would normally think of as having a reason.

I seem to recall it follows from Maxwell's equations, but that's not really a reason, is it?

 

[col]

Why questions are notoriously difficult to avoid just saying "because thats the way they behave"

How about - potential energy of the two charges increases when they repel each other and decreases when they attract each other. PE is positve for charges of the same sign and negative for charges of opposite sign (goes as product of the charges) and inversely prop to their separation so it decreases when like charges separate and unlike charges move together.

or saying the same thing a different way


The force is proportional to the product of the charges so its in a positive direction when they have the same sign ie acts as a repulsion and in a negative direction when they have opposite signs.

Its easier drawing diagrams and graphs

 

[RoddyVR]

because electrons and protons REALY dislike inbreeding, so when there's extra of one of them in two "pieces" then they try to stay away, but if there's extra one of electrons in one and protons in the other then they head for eachother like there's no tomorow.

sorry, couldnt help it. you wanted a clean answer, i didnt know it, so i gave a dirty one.

 

[Gothmog]

Opposite-charged particles attract because their fields cancel one another more and more the closer they are together. Similarly charged particles repel because their fields can only add. The energy stored in the field is proportional to the field strength squared, and the force is in the direction that would reduce the energy stored in the sum of their two coulomb fields if the particles moved in the direction of that force.

As soon as either particle actually moves photons are emitted and the whole picture becomes more complicated. I wont try to touch that one.

 

[betazed]

It does not follow from maxwell's equations.

Maxwell's equations assume it. If the forces were reversed Maxwell's equations will still hold. We will just have some signs changed here and there. That's about all.

 

[The Last Conformist]

Well, the signs in ME are experimentally verified. I expected a better shooting down of that answer.

 

[betazed]

The energy and field picture (which are both essentially the same) that Gothmog and Col stated really begs the question "why they are so"? {because that is exactly the content of Maxwell's equation as I stated in the last post}

Gothmog said:

As soon as either particle actually moves photons are emitted and the whole picture becomes more complicated. I wont try to touch that one.

The answer lies there.

 

[Kinniken]

Do we even know why? Or is the "answer" only moving the question a level deeper?

I agree with Col, this question does not seem to have a finite answer.

 

[col]

Building on my last answer, it takes work / energy to separate opposite charges so we know they attract.

Anthropic answer - if they didnt attract there could be no atoms and we wouldnt be here to ask the question.

 

[betazed]

Originally posted by The Last Conformist
Well, the signs in ME are experimentally verified. I expected a better shooting down of that answer.

I am not shooting down your answer. I am saying you did not answer my question (because my question could be stated another way as why are the signs in maxwell's equation such as they are?) .

 

[MikeLynch]

Why do like charges repel and opposite charges attract?

Because the Lord Jesus Our God wills it to be so.

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