Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How many are there?

  1. Aug 4, 2005 #1
    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?
  2. jcsd
  3. Aug 4, 2005 #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.
  4. Aug 4, 2005 #3

    Claude Bile

    User Avatar
    Science Advisor

    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.

  5. Aug 5, 2005 #4
    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.
  6. Aug 5, 2005 #5
    you are forgetting a law here, see the above post

  7. Aug 5, 2005 #6
    But i don't know why we can not reach the zero absolute temperature. Who can explain?
  8. Aug 7, 2005 #7

    Claude Bile

    User Avatar
    Science Advisor

    Essentially, because a particle at 0K violates the HUP. Google the 3rd law of thermodynamics and you should find some satisfying explanations.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: How many are there?