How many are there?

  • Thread starter LENIN
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  • #1
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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

  • #2
211
2
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.
 
  • #3
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.
 
  • #4
125
2
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.
 
  • #5
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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
 
  • #6
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But i don't know why we can not reach the zero absolute temperature. Who can explain?
 
  • #7
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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