648 reputation
514
bio website kemiisto.ru
location Oslo, Norway
age 28
visits member for 3 years, 8 months
seen 28 mins ago

1d
accepted Where is the potential energy due to internal interactions in total energy?
1d
comment Where is the potential energy due to internal interactions in total energy?
Regarding the second point, does it mean that when in statistical mechanics we write down internal energy as the weighted sum of all microstate energies $U = \sum_{i=1}^N p_i E_i$ the potential energy due to macroscopic interactions is actually already ignored?
1d
awarded  Curious
1d
revised Where is the potential energy due to internal interactions in total energy?
added 45 characters in body
1d
comment Where is the potential energy due to internal interactions in total energy?
I rewrote the question. Now it is the following. When the first law refers to internal energy as a state function increase in which is equal to heat supplied to the system plus work done on it, does this state function include potential energy due to gravitational interactions within the system?
1d
revised Where is the potential energy due to internal interactions in total energy?
deleted 782 characters in body
1d
revised Where is the potential energy due to internal interactions in total energy?
added 1191 characters in body
1d
comment Where is the potential energy due to internal interactions in total energy?
Let us continue this discussion in chat.
1d
revised Where is the potential energy due to internal interactions in total energy?
added 1191 characters in body
1d
revised Where is the potential energy due to internal interactions in total energy?
added 1191 characters in body
1d
comment Where is the potential energy due to internal interactions in total energy?
In other words, intuition tells me that gravitational (or any other kind of) interaction between macroscopic bodies in a thermodynamic system does not contribute to its internal energy (at least in thermodynamic meaning of these quantity). But I could not find information about it in books.
1d
comment Where is the potential energy due to internal interactions in total energy?
@ticster this phrase can be found in many books on thermodynamics. But it is wrong for a system consisting of more than 1 macroscopic body, since there is a potential energy due to gravitational interaction of the bodies which is not counted according to this definition at all. Unless this energy is part of internal energy.
1d
comment Where is the potential energy due to internal interactions in total energy?
@ticster I'm not a physicist, but I have a feeling that your very last equation is right. Then, however, there is a problem with thermodynamic notion of internal energy as I know it, which refers to energy contained within the system, and excludes kinetic energy of motion of the system as a whole, and the potential energy of the system as a whole due to external force fields.
1d
comment Where is the potential energy due to internal interactions in total energy?
@ticster I'm talking about a thermodynamic system, which is macroscopic by definition. It is not a two particle system, rather it consists of myriads of particles in two macroscopic pieces of bulk matter. And these pieces interact with each other thorough gravity.
2d
comment Where is the potential energy due to internal interactions in total energy?
Hmmm... The definition of internal energy which you give is surprising for me. In classical thermodynamics internal energy is just a state function the increase in which for a closed system during a thermodynamic process is equal to the heat supplied to the system plus the work done on the system. From a microscopic point of view of statistical thermodynamics it is the kinetic energy of particles motion and potential energy due to all kinds of interaction between particles in a system.
2d
asked Where is the potential energy due to internal interactions in total energy?
Jul
19
awarded  Yearling
Jul
19
revised What is the complete quantum description of a free electron
added 382 characters in body
Jul
19
comment What is the complete quantum description of a free electron
I agree with @LuboŇ°Motl. I think $m$ and $q$ belongs to the definition of the system, rather than to the description of its state. Although, I've read somewhere, that in QFT $m$ and $q$ are treated as observables with corresponding operators. And that superpositions of eigenstates of this operators aren't physically realizable since they are forbidden by the superselection rules, whatever they are...
Jul
19
revised What is the complete quantum description of a free electron
added 69 characters in body