How many are there?

  • Thread starter LENIN
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Main Question or Discussion Point

How many laws of thermodinamics are there?

This topic came up during one of our last hours of higschool physics. Some of us sead that there are 4 and some sead that there are only 2. In different books we also found different answeres. So now I realy don't know which statement is corect. Any ideas?
 

Answers and Replies

211
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There are four laws of thermodynamics but they are numbered funny.

The first three were discovered, then someone decided there was an implicit assumption in those 3 that required a definition of temperature, so the fourth law discovered is numbered zero.
 
Claude Bile
Science Advisor
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0th law - If a system, C is in thermal equilibrium with two other systems, A and B, then A and B must also be in thermal equilibrium.

1st law - Heat = Change in Internal Energy + Work done on the system. (Conservation of energy effectively).

2nd law - Entropy always increases with time.

3rd law - No object can ever reach a temperature of absolute zero.

A nice discussion of laws 1-3 can be found here.
http://www.physlink.com/Education/AskExperts/ae280.cfm

Claude.
 
125
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1st Law: You can't win; you can only break even

2nd Law: You can only break even if you get to absolute zero.

3rd Law: You can't get to absolute zero.
 
3,761
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rdt2 said:
1st Law: You can't win; you can only break even

2nd Law: You can only break even if you get to absolute zero.

3rd Law: You can't get to absolute zero.
you are forgetting a law here, see the above post

marlon
 
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But i don't know why we can not reach the zero absolute temperature. Who can explain?
 
Claude Bile
Science Advisor
1,471
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Essentially, because a particle at 0K violates the HUP. Google the 3rd law of thermodynamics and you should find some satisfying explanations.

Claude.
 

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