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Author Topic: 4th law of thermodynamics?  (Read 2140 times)

siochi

• Jr. Member
• Posts: 49
4th law of thermodynamics?
« on: 19/08/2011 10:34:48 »
I was studying about the laws of thermodynamic back at school, and I happened to have an argument regarding the second law of thermodynamic. According to the 2nd law of thermodynamic, no machine can be 100 % efficient.

In reply to that, I created the 4th law of thermodynamic, which states that "Every machine is the most efficient (100% ) at doing what it does. "

Do you agree with that? Is there any logical error?

MikeS

• Neilep Level Member
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4th law of thermodynamics?
« Reply #1 on: 19/08/2011 11:11:54 »
I was studying about the laws of thermodynamic back at school, and I happened to have an argument regarding the second law of thermodynamic. According to the 2nd law of thermodynamic, no machine can be 100 % efficient.

In reply to that, I created the 4th law of thermodynamic, which states that "Every machine is the most efficient (100% ) at doing what it does. "

Do you agree with that? Is there any logical error?

The error comes about by how you define 100% efficiency and in relation to what.

For example, a chemical process could be 100% efficient in producing chemical energy but only 1% efficient when viewed from the nuclear production of energy.
« Last Edit: 19/08/2011 11:19:41 by MikeS »

imatfaal

• Neilep Level Member
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• rouge moderator
4th law of thermodynamics?
« Reply #2 on: 19/08/2011 11:53:13 »
Siochi

Your formulation of the 2nd law is a bit constrained and incomplete.  try reading up at these two sites which give the more general view
http://en.wikipedia.org/wiki/Second_law_of_thermodynamics#Informal_descriptions
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/seclaw.html

Personally I cannot see any difference between your cut down version of the 2nd and your fourth law.

Mike
Can a chemical reaction ever take place that is 100pct efficient?  I would have thought that was precluded by either waste heat in an exothermic reaction or misuse of heat in an endothermic qv lord kelvin's definition of 2nd law

Bored chemist

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4th law of thermodynamics?
« Reply #3 on: 20/08/2011 00:01:45 »
"Every machine is the most efficient (100% ) at doing what it does. "

My friend bill has two cars; they both transport him from a to b , but one of them takes twice as much petrol as the other because it's got an old clapped out engine; it is, therefore, half as efficient.

"the great tragedy of Science - the slaying of a beautiful hypothesis by an ugly fact"

Or are you taking the view that one of the things that the thirsty  engine does is heat the area and, if you take that into account it does a better job than the other?
If you are then your assertion simply becomes a truism.

MikeS

• Neilep Level Member
• Posts: 1044
4th law of thermodynamics?
« Reply #4 on: 20/08/2011 07:27:52 »
imatfaal

You'r right of course, I was just using it as a comparison.

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4th law of thermodynamics?
« Reply #4 on: 20/08/2011 07:27:52 »