About Ensemble Average for gas molecules(classical mechanics regime)

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SUMMARY

The discussion focuses on the concept of Ensemble Average in classical mechanics, specifically regarding gas molecules. It establishes that macroscopic variables of fluids are averages of microscopic variables of gas molecules. The concept of ergodicity is introduced, where time averages equal spatial averages. The participant questions whether different microscopic variables, such as center of mass, momentum, and translational energy, can be considered the same state from a macroscopic perspective if they share the same average value, emphasizing the relationship between microstates and macrostates in thermodynamics.

PREREQUISITES
  • Understanding of classical mechanics principles
  • Familiarity with thermodynamics concepts
  • Knowledge of statistical mechanics
  • Basic grasp of ergodicity in physics
NEXT STEPS
  • Study the implications of ergodicity in statistical mechanics
  • Explore the relationship between microstates and macrostates in thermodynamics
  • Investigate the role of entropy in determining macroscopic states
  • Learn about different types of averages in statistical physics
USEFUL FOR

Students and professionals in physics, particularly those studying statistical mechanics, thermodynamics, and classical mechanics, will benefit from this discussion.

Noh-hoon Lee
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I have some question about Ensemble Average.

The macroscopic variable of fluid is average of microscopic variable of gas molecule.

And if time average is same with spatial average I know as it called edgodic.

My question is that if two different microscopic variables which have same average value, like center of mass, momentum, translational energy, (angular momentum has some error but it is very small so I ignore it.(it is acceptable error))

Does it can be seen as a same state for macroscopic view?
 
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Every microstate is unique configuration of particle states and. In pursuit of thermodynamics, we say that there are many different microstates for the same macrostate, so long as they have the same ensemble averages. The number of microstates for a given macrostate determines its entropy, and from there, all the rest of thermodynamics can follow.


Noh-hoon Lee said:
I have some question about Ensemble Average.

The macroscopic variable of fluid is average of microscopic variable of gas molecule.

And if time average is same with spatial average I know as it called edgodic.

My question is that if two different microscopic variables which have same average value, like center of mass, momentum, translational energy, (angular momentum has some error but it is very small so I ignore it.(it is acceptable error))

Does it can be seen as a same state for macroscopic view?
 
thank you for your reply :) It's really helpful
 

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