# How many are there?

LENIN
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 really don't know which statement is corect. Any ideas?

mmwave
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.

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.

Claude.

rdt2
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.

marlon
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

pocoman
But i don't know why we can not reach the zero absolute temperature. Who can explain?