PDA

View Full Version : The Laws of Thermodynamics



Glom
2004-Mar-08, 09:09 PM
Just checking what's what.

Zeroth law.
Absolute zero cannot be experimentally reached.

First law.
Energy can neither be created nor destroyed.

Second law.
100% efficiency is not attainable.

Drakheim
2004-Mar-08, 09:34 PM
Just checking what's what.

Zeroth law.
Absolute zero cannot be experimentally reached.

First law.
Energy can neither be created nor destroyed.

Second law.
100% efficiency is not attainable.

You have it right so far.

xbck1
2004-Mar-08, 09:35 PM
<--Not sure if the last one is a joke or not.
<--Pretty sure it's not.

Why isn't Abolute Zero unattainable experimentally? Because you'd need a perfect vacuum and such?

Of course 100% efficiency isn't attainable! Not with things like Tetris, Solitare and the penguin and yeti game available to your employees!

Sticks
2004-Mar-08, 09:37 PM
don't forget pinball with Windows 2000 or XP

can anything with Microsoft Windows be 100% efficient :lol:

George
2004-Mar-08, 09:48 PM
Just checking what's what.
Second law.
100% efficiency is not attainable.

Of course, as a result, this means many things.

My favorite version is..."heat won't flow from a cooler to a hotter, you can try if you like, but you far better notter!" - my old thermo book - Simmang.

Drakheim
2004-Mar-08, 09:59 PM
Why isn't Abolute Zero unattainable experimentally? Because you'd need a perfect vacuum and such?


Well, you first need an environment that is not going to be influenced by the outside conditions.

Then you need to be able to achieve absolute zero conditions in that environment.

Now even if you could do the above, it would be next to impossible to confirm it since any instruments that would measure the conditions in there would cease to function when the temp reaches 0 K.

So while in theory you can achieve it, you will never be able to prove it.

cyswxman
2004-Mar-08, 10:16 PM
On this board we obey the Laws of Thermodynamics!!!! :wink: :wink:

Glom
2004-Mar-08, 10:19 PM
Classically, I believe the rule goes that in order to reach absolute zero, you'd need to have something below absolute zero to take the heat away, which is of course nonsensical.

Quantumly, absolute zero defies the Heisenberg Uncertainty Principle. In order that we not know exactly how fast a particle is moving, even at lowest energy states, it still has energy and hence motion, called zero point fluctuations. Also, even if you could get to absolute zero, you couldn't know it because you'd have to bombard the particle with energy to detect it and hence setting it in motion again.

George
2004-Mar-08, 10:21 PM
As I vaguely recall, entropy is applied to get to extremely low temperatures. I want to say the mass is given magnetic alignment then, after cooling further, the magnet is removed creating disorder and ejecting heat. (Or am I even close?)

swansont
2004-Mar-08, 10:27 PM
Just checking what's what.

Zeroth law.
Absolute zero cannot be experimentally reached.

First law.
Energy can neither be created nor destroyed.

Second law.
100% efficiency is not attainable.

You have it right so far.

No, the zeroth law is thermal equilibrium: if A and B are at the same temperature, and B and C are at the same temperature, then A and C are at the same temperature.

It's the third law that states that absolute zero cannot be reached by any finite process.


Then there's the fourth law: beer is good

fifth law: men turn into (derogatory anatomical epithet)s when driving sports cars

sixth law: 90% of everything is crud.

Drakheim
2004-Mar-08, 10:30 PM
Dont forget law #7

All rules are inherently made by women and therefore are subject to change without notice or approval.

Swift
2004-Mar-08, 10:59 PM
I always liked this version of the three laws (not including the zeroth):
- you can't win
- you can't break-even
- you can't get out of the game.

http://www.physlink.com/Education/AskExperts/ae280.cfm
http://en.wikipedia.org/wiki/Thermodynamics

Some alternative, serious definitions:

First Law: Energy Can Be neither Created nor Destroyed
Second Law: The Entropy of an Isolated System always Increases
Third Law: The Entropy of a Perfect Crystal at Absolute Zero is Zero

Zeroth law: Thermodynamic equilibrium. If A and B are in thermodynamic equilibrium, and B and C are in thermodynamic equilibrium, then A and C are also in thermodynamic equilibrium.
1st Law: Conservation of energy.
2nd Law: It is impossible to obtain a process such that the unique effect is the subtraction of a positive heat from a reservoir and the production of a positive work. Specifically, A system operating in contact with a thermal reservoir cannot produce positive work in its surroundings (Kelvin)
3rd Law: All processes cease as temperature approaches zero.

ToSeek
2004-Mar-08, 11:13 PM
sixth law: 90% of everything is crud.

There is NO law 6!

George
2004-Mar-08, 11:22 PM
I always liked this version of the three laws (not including the zeroth):
- you can't win
- you can't break-even
- you can't get out of the game.

http://www.physlink.com/Education/AskExperts/ae280.cfm
http://en.wikipedia.org/wiki/Thermodynamics

Some alternative, serious definitions:

First Law: Energy Can Be neither Created nor Destroyed
Second Law: The Entropy of an Isolated System always Increases
Third Law: The Entropy of a Perfect Crystal at Absolute Zero is Zero

Zeroth law: Thermodynamic equilibrium. If A and B are in thermodynamic equilibrium, and B and C are in thermodynamic equilibrium, then A and C are also in thermodynamic equilibrium.
1st Law: Conservation of energy.
2nd Law: It is impossible to obtain a process such that the unique effect is the subtraction of a positive heat from a reservoir and the production of a positive work. Specifically, A system operating in contact with a thermal reservoir cannot produce positive work in its surroundings (Kelvin)
3rd Law: All processes cease as temperature approaches zero.

Kelvin's 2nd law is odd to me. By "reservoir" does he mean "sump" (waste heat)? Many process utilize a thermal source for producing work. Oh wait, I see, he means 100% conversion from heat to work can not be accomplished. Key word here is "unique". 8)

I really like "can't get out of the game". More gripping than usual. :)

freddo
2004-Mar-08, 11:36 PM
On this board we obey the Laws of Thermodynamics!!!! :wink: :wink:

We sure do... =D>

Wiley
2004-Mar-09, 12:03 AM
sixth law: 90% of everything is crud.

There is NO law 6!

Thanks for the reminder, Bruce. :D

George
2004-Mar-09, 12:14 AM
sixth law: 90% of everything is crud.

There is NO law 6!

Thanks for the reminder, Bruce. :D

[-X When in doubt...see rule 7!

Kaptain K
2004-Mar-09, 06:40 AM
sixth law: 90% of everything is crud.
This is also known as Sturgeon's Law.

Diamond
2004-Mar-09, 08:56 AM
On this board we obey the Laws of Thermodynamics!!!! :wink: :wink:

"...and Lisa, we obey the Laws of thermodynamics IN THIS HOUSE" - Homer J. Simpson

Edit: Incidentally, this is one of the reasons why I doubt the reports of an accelerating force in the Universe (or the so-called Cosmological Constant). If it were so, where would the energy come from? Would not the effect of this energy be to reduce the entropy of the Universe?

eburacum45
2004-Mar-09, 10:43 AM
I agree with you there, Diamond;

The laws of thermodynamics are descriptive, not prescriptive; they are indispensible to physics and engineering, yet the universe as a whole does not seem to follow them.

Consider this;
the cosmological constant implies a force existing in empty space exerting a pressure on the universe itself which causes it to expand; in one model I have encountered, the force remains the same per unit volume -but the number of unit volumes is increasing -!

So the universe becomes an enormous free lunch, which gets bigger while you are eating it.

Where are your laws of thermodynamics now, Lord Kelvin?

swansont
2004-Mar-09, 10:54 AM
sixth law: 90% of everything is crud.
This is also known as Sturgeon's Law.

Thanks - I did not know that!

I also like Hofstadter's law: It alsways take longer than you think, even when you take into account Hofstadter's law.

Iain Lambert
2004-Mar-09, 11:08 AM
Then there's Godwin's Law, as demonstrated on 'certain' fora on a regular basis:

"As an internet discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one." Its then standard procedure that the side making said comparison is considered to have lost.

Andromeda321
2004-Mar-09, 01:19 PM
Oooo, physics moment!
Today in economics we were discussing renewable energy sources. Class was going along fine and dandy until I pointed out that, according to the second law of thermodynamics, no energy source is truly reusable and everything we do still contributes to the heat death of the universe (yay for entropy!).
My teacher's response, "you know, up until now I was going to congratulate you at the end of the period for being unusually focused today..."

Swift
2004-Mar-09, 01:53 PM
On this board we obey the Laws of Thermodynamics!!!! :wink: :wink:

"...and Lisa, we obey the Laws of thermodynamics IN THIS HOUSE" - Homer J. Simpson
I always wanted to get t-shirts made up, one with Newton, one with Einstein, in the Uncle Sam pose, with the quote "Gravity, it's not a good idea, it's the LAW!" :D

Glom
2004-Mar-09, 02:17 PM
Oooo, physics moment!
Today in economics we were discussing renewable energy sources. Class was going along fine and dandy until I pointed out that, according to the second law of thermodynamics, no energy source is truly reusable and everything we do still contributes to the heat death of the universe (yay for entropy!).
My teacher's response, "you know, up until now I was going to congratulate you at the end of the period for being unusually focused today..."

Say what? Your teacher didn't congratulate you because you forced a realisation that ultimately everything is subject to the laws of physics?

I hate people who think their political motives are so high and mighty they can disregard science.

Normandy6644
2004-Mar-09, 04:07 PM
What she didn't mention was that after she made mention of physics, she threw an apple at the teacher to prove that Newton was right.

George
2004-Mar-09, 07:19 PM
Oooo, physics moment!
Today in economics we were discussing renewable energy sources. Class was going along fine and dandy until I pointed out that, according to the second law of thermodynamics, no energy source is truly reusable and everything we do still contributes to the heat death of the universe (yay for entropy!).
My teacher's response, "you know, up until now I was going to congratulate you at the end of the period for being unusually focused today..."

Ironically, entropy seems to working with your teachers mental process. To bad you are getting the "heat". :wink:

Maksutov
2004-Mar-10, 09:15 AM
Oooo, physics moment!
Today in economics we were discussing renewable energy sources. Class was going along fine and dandy until I pointed out that, according to the second law of thermodynamics, no energy source is truly reusable and everything we do still contributes to the heat death of the universe (yay for entropy!).
My teacher's response, "you know, up until now I was going to congratulate you at the end of the period for being unusually focused today..."

So your economics teacher needed all those words, which included an ad hominem, to say, "I don't understand what you said."?

I bet balancing a checkbook is more than that teacher can handle! :roll: