The second law of thermodynamics says that when energy changes from one form to another form, or matter moves freely, entropy (disorder) in a closed system increases.
Differences in temperature, pressure, and density tend to even out horizontally after a while. Due to the force of gravity, density and pressure do not even out vertically. Density and pressure on the bottom will be more than at the top.
Entropy is a measure of spread of matter and energy to everywhere they have access.
The most common wording for the second law of thermodynamics is essentially due to Rudolf Clausius:
In other words, everything tries to maintain the same temperature over time.
There are many statements of the second law which use different terms, but all mean the same thing. Another statement by Clausius is:
Heat cannot of itself pass from a colder to a hotter body.
A transformation whose only final result is to convert heat, extracted from a source at constant temperature, into work, is impossible.
The second law only applies to large systems. The second law is about the likely behavior of a system where no energy or matter gets in or out. The bigger the system is, the more likely the second law will be true.
Questions and Answers
Q: What is the second law of thermodynamics?
A: The second law of thermodynamics states that when energy changes from one form to another form, or matter moves freely, entropy (disorder) in a closed system increases.
Q: What tends to even out horizontally over time?
A: Differences in temperature, pressure, and density tend to even out horizontally after a while.
Q: Why do density and pressure not even out vertically?
A: Due to the force of gravity, density and pressure do not even out vertically. Density and pressure on the bottom will be more than at the top.
Q: What is entropy?
A: Entropy is a measure of spread of matter and energy to everywhere they have access.
Q: What is the most common wording for the second law of thermodynamics?
A: The most common wording for the second law of thermodynamics is essentially due to Rudolf Clausius: everything tries to maintain the same temperature over time.
Q: What is another statement by Clausius regarding the second law of thermodynamics?
A: Another statement by Clausius is that heat cannot of itself pass from a colder to a hotter body.
Q: To what kind of system does the second law of thermodynamics apply?
A: The second law of thermodynamics only applies to large systems, where no energy or matter gets in or out. The bigger the system is, the more likely the second law will be true.
