Science Quiz

[Renata]

So who gets the next question?

<-- has question all fired up and ready to go

Renata

 

[col]

Go ahead Renata

 

[Renata]

Oh goody.

Why is ice slippery?

Ren

 

[Kinniken]

Isn't that a bit vague?? Is saying that it's due to the very law friction between ice and most solid enough?

 

[The Last Conformist]

Because except at extremely low temperatures (at which ice isn't slippery), it's always got a thin coating of liquid temperatures, which has much the same effect as machine oil to decrease friction.

 

[Renata]

Well, that didn't take long. I was expecting at least one person to try to ascribe it to pressure-melting or friction-melting, but can't win 'em all.

TLC got it. Roughly speaking, the surface of ice is composed of dangling bonds that are constantly shifting and moving around, making layers of what is, in effect, liquid water. So you get the same effect stepping on ice as you get stepping in a puddle on a smooth tile floor.

Kinniken, your answer just begged the question: *why* is the friction so low?

I like surface chemistry -- lots of surprising results.

Next!

Renata

 

[Kinniken]

Originally posted by Renata
Kinniken, your answer just begged the question: *why* is the friction so low?

I thought of adding the part about the thin coat of liquid water, but that only begged the question: *why* does having a coat of liquid water makes the friction so low?

 

[The Last Conformist]

I hate solid state only with slightly less passion than those annoying intermediate forms. Don't those darned chemicals release the Ideal Gas Law effected for a reason?

A couple of billions of years ago, a number of natural fission reactors form in Oklo in modern Gabon, "burning" uranium just the same way as a nuclear power plant. No such natural reactors could form today - why?

 

[betazed]

Originally posted by The Last Conformist


A couple of billions of years ago, a number of natural fission reactors form in Oklo in modern Gabon, "burning" uranium just the same way as a nuclear power plant. No such natural reactors could form today - why?

Bacause the concentration of natural Uranium is now below the critical mass required for natural fission owing to radioactive decay?

 

[Garvarg]

Too many union safety precautions.

 

[The Last Conformist]

The uranium concentration is restored each time a uranium-containing mineral is formed, which kind of processes still goes on. Try again.

 

[Kinniken]

It would get bombed in a preventive strike?

More seriously, I would answer like betazed... The concentration of Uranium is no longer sufficient.

edit cross-posted. Then I guess that the reason is not a matter of concentration, but of too much of the U235 has decayed.

 

[nonconformist]

Most of the Uranim has decayed?

 

[Kinniken]

Hmm, if that's the answer who was first?

 

[betazed]

Originally posted by The Last Conformist
The uranium concentration is restored each time a uranium-containing mineral is formed, which kind of processes still goes on. Try again.

Hmmmm....

So I did a few google searches and came up with this

http://www.earlham.edu/~graliza/oklo.htm

It seems what I said was essentially right.

The uranium was concentrated by a series of geological quirks and then continued till uranium density decayed below a certain limit. Something like this cannot happen today because most of earth's fissile uranium has decayed owing to radioactivity.

 

[The Last Conformist]

Kinniken is right - the percentage of U235 in natural uranium is too low nowadays.

betazed: Your link confirms that it is the isotope composition which matters.

 

[betazed]

You are right. I should have been more precise.

 

[Kinniken]

Who was the first person to measure the circumference of the Earth with a reasonable accuracy?

 

[The Last Conformist]

Eratosthenes

 

[nonconformist]

Ferdinand Magellan?