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Author Topic: What is Entropy ? εντροπία  (Read 4578 times)

ScientificBoysClub

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What is Entropy ? εντροπία
« on: 22/01/2009 14:06:57 »
What is Entropy ?   :o [8D] ??? ::)

Could any one  PLz explain me what is Entropy ?

In my physics text book the def is like this ..
It's a thermal property that remains constant during Adiabatic process or Isothermal ??

s=q/t ??? q is heat ... and t is temperature ........ plz help me why Q/t ?? temperature is measure of heat ?? why ? Q/T ??

PLZ give me good examples ?? Easy one ??


 

Offline Vern

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What is Entropy ? εντροπία
« Reply #1 on: 22/01/2009 14:14:41 »
Good old Google has a bunch of definitions depending upon the system you are studying.
 

ScientificBoysClub

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What is Entropy ? εντροπία
« Reply #2 on: 22/01/2009 14:16:03 »
Good old Google has a bunch of definitions depending upon the system you are studying.
yeah I know ....... but plz here we discuss about it right not good old google ?? PLz give u r own def ??
 

Offline Vern

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What is Entropy ? εντροπία
« Reply #3 on: 22/01/2009 14:30:52 »
Entropy is the process of a system going from its present state to a less complex or less energetic state. For example going from hot to cold. That's just my simple take on it.
 

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What is Entropy ? εντροπία
« Reply #4 on: 22/01/2009 14:32:32 »
Entropy is the process of a system going from its present state to a less complex or less energetic state. For example going from hot to cold. That's just my simple take on it.
thanks science dude ??!! .... so, it's nothing but failure of a system to maintain its own energy state as original level right ?
 

Offline Vern

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« Reply #5 on: 22/01/2009 14:55:39 »
I don't know if you could call it "failure". It is just the natural way things work; as far as we know everything tends toward that lesser state.
 

Offline LeeE

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« Reply #6 on: 23/01/2009 00:42:23 »
Pesonally, I really don't like definitions of entropy that rely upon 'information' because information is subjective.  Anyone that has paid a lot of money for a Jackson Pollack original would certainly disagree with most of the 'information' based definitions of entropy.

Entropy is the tendency of energy to run downhill; in practice, to equalise with a lower energy level.
 

Offline yor_on

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What is Entropy ? εντροπία
« Reply #7 on: 23/01/2009 16:19:31 »
Entropy is a strange concept:)
"A function first introduced in classical thermodynamics to provide a quantitative basis for the common observation that naturally occurring processes have a particular direction.
 
Subsequently, in statistical thermodynamics, entropy was shown to be a measure of the number of microstates a system could assume.
 
Finally, in communication theory, entropy is a measure of information."

One could see it as belonging to the arrow of time.

'Fresh' new energy can be used in various ways, but after it has been 'used' it will degrade into something  much more difficult to transform into 'new work'.

It also goes back to the idea that nothing in our universe ever is 'lost'.
Energy only gets transformed and in that process more and more equalized and 'un-useful'.

But if one could proof that something do gets lost (from our universe) then I think we would have to find a new definition for it.
 

Offline lightarrow

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« Reply #8 on: 23/01/2009 17:04:27 »
Pesonally, I really don't like definitions of entropy that rely upon 'information' because information is subjective.  Anyone that has paid a lot of money for a Jackson Pollack original would certainly disagree with most of the 'information' based definitions of entropy.

Entropy is the tendency of energy to run downhill; in practice, to equalise with a lower energy level.
Do you mean as an iron ball going down a hill without friction?
However there is no need to talk about information, we can simply talk (at a very simple level) of 'state of more or less order'.
« Last Edit: 23/01/2009 17:06:14 by lightarrow »
 

Offline LeeE

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What is Entropy ? εντροπία
« Reply #9 on: 23/01/2009 23:14:28 »
Quote
However there is no need to talk about information, we can simply talk (at a very simple level) of 'state of more or less order'.

That's what I was referring to with the mention of Jackson Pollack.  If we spill a can of paint on the floor most people would say it is less ordered, but if JP does so, it is apparently not.

It's best to stick with energy based definitions of Entropy, imo.
 

Offline DoctorBeaver

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« Reply #10 on: 23/01/2009 23:18:53 »
I must admit I get a bit confused by entropy. I thought I had it cracked but my hopes were soundly dashed by, I believe, SoulSurfer  :(
 

Offline lightarrow

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« Reply #11 on: 24/01/2009 12:14:00 »
Quote
However there is no need to talk about information, we can simply talk (at a very simple level) of 'state of more or less order'.

That's what I was referring to with the mention of Jackson Pollack.  If we spill a can of paint on the floor most people would say it is less ordered, but if JP does so, it is apparently not.

It's best to stick with energy based definitions of Entropy, imo.
But if you define it in that way it's even more ambiguous: entropy doesn't vary when an iron ball goes downhill without friction, but in that case you could say that energy has the tendency to run downhill, I presume.

I prefer the microscopic definition: S = kB*ln(w)
w = number of different possible configurations (microstates) in which the state can be.
kB = Boltzmann's constant.
So, the greater the number of configurations, the less ordered is the system. Here the concept of information is not used.
« Last Edit: 24/01/2009 12:16:38 by lightarrow »
 

Offline LeeE

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« Reply #12 on: 24/01/2009 21:15:23 »
Hmm...  it's seems to me that 'entropy' can be used to describe two different things, or at least, can be applied at two different levels.

To be honest, it really only means anything to me in terms of energy gradients - yes, the tendency for energy to 'run downhill'.  So, were it not for entropy, energy could move from any level to any other level regardless of direction, and nothing would work very well; turn the kettle on to make a cup of coffee and even if the heating element got hot, the water might not.  In this respect, I see it solely as a fundamental principle, required for causality, and not as a measure of something.

On the other hand though, it's use to describe the degree of order in something always seems to need other factors to be taken in to account, although I may be misinterpreting it's use correctly.  For example, take two tins of paint.  One of them has solidified while the other is still runny.  Would the solidified tin of paint be more or less ordered than the runny tin?  To me, the difference between the two is better described by the different chemical states of the contents, which comes down to movement of energy, rather than saying one is more ordered than the other.

Perhaps there's something about entropy that I just don't get - I see little practical use in saying that one system is more ordered than another when the difference between them, at the bottom line, is due to how energy has moved.
 

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What is Entropy ? εντροπία
« Reply #12 on: 24/01/2009 21:15:23 »

 

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