Energetically favorable configuration

[Danijel Gorupec]

A quickie... What does the term 'energetically favorable configuration' means? Does it have any strict meaning at all?

One might say, for example: "magnetic domains will set into an energetically favorable configuration" (but my question is general, not about magnetic domains in ferromagnetic materials).

(If it means 'lowest possible energy' then I guess that closed systems cannot have 'energetically favorable configuration' as the energy there is conserved)

[studiot]

22 minutes ago, Danijel Gorupec said:

A quickie... What does the term 'energetically favorable configuration' means? Does it have any strict meaning at all?

One might say, for example: "magnetic domains will set into an energetically favorable configuration" (but my question is general, not about magnetic domains in ferromagnetic materials).

(If it means 'lowest possible energy' then I guess that closed systems cannot have 'energetically favorable configuration' as the energy there is conserved)

Could have one of two meanings.

Firstly it usually means that the process can proceed by itself and thus there is net evolution of energy.
This is called spontaneous.

If the process requires energy then energy to proceed then it is driven or forced and will not be spontaneous.
 

In this way it is not 'energetically favourable'.

 

Remember also that a closed system does not means closed to energy.
It means closed to mass exchange.

An isolated system is closed to both mass and energy exchange.

You can also have a pseudo closed system (flow system) where the same amount of mass enters a system as leaves duting the process so there is no net exchange of mass.

This is how heat exchanger work.

 

Does this help?

[Danijel Gorupec]

12 minutes ago, studiot said:

Does this help?

Actually yes; thank you. It introduces the concept of 'evolution of energy' which I find more intuitive than the 'energetically favorable configuration'.

But I guess there is some misalignment in your answer and my question - you are talking about 'energetically favorable process', while I ask for 'energetically favorable configuration'. I can guess, from your answer, that the 'energetically favorable configuration' could mean that a system reached a state where there is no more net evolution of energy - could this be right?

(Yes, I had to write 'isolated system' instead of 'closed system' - I guess i my language we use the same term for both things).

[studiot]

1 hour ago, Danijel Gorupec said:

Actually yes; thank you. It introduces the concept of 'evolution of energy' which I find more intuitive than the 'energetically favorable configuration'.

But I guess there is some misalignment in your answer and my question - you are talking about 'energetically favorable process', while I ask for 'energetically favorable configuration'. I can guess, from your answer, that the 'energetically favorable configuration' could mean that a system reached a state where there is no more net evolution of energy - could this be right?

(Yes, I had to write 'isolated system' instead of 'closed system' - I guess i my language we use the same term for both things).

Fair comment, I did say there were two possible meanings.

The second one is context sensitive and I prefer not to use it.

 

Consider a pendulum with a rigid arm.

When it is hanging down with the bob vertically below the pivot it is in a condition of lowest potential energy compared to any other position.

You may consider the position as meaning a configuration of the system.

If the bob is not actually moving, but just hanging there then there is no kinetic energy.

The bob could hang there indefinitely unless disturbed by an outside force.

The system is in equilibrium.

If disturbed slightly the bob will rapidly return to the equilibrium position (although it will overshoot and thus oscillate).

Such an equilibrium position is called a stable equilibrium position.

 

Now consider the bob vertically above the pivot.

The bob could, in theory remain there indefinitely because it is also in equilibrium.

But this equilibrium is different in two ways from the lower configuration.

Firstly if the bob is disturbed, even minutely, it will accelerate rapidly away from this equilibrium position.

This is called unstable equilibrium.

Secondly the bob has greater potential energy than in the lower position.

The system now moves towards the configuration of stable equilibrium.

In general, a configuration of unstable equilibrium has greater potential energy than one in stable equilibrium.

So we say that moving from an unstable to a stable equilibrium configuration is 'energetically favourable'.

But watchout because in this case the system does not evolve (or loose) energy.

The loss of potential energy is matched by the gain in kinetic energy of the bob.

So in my first case the energy of the system is diminished by energy favourability, so the loss of energy provides the 'driving force' causing the change.

In the second case there is no driving force internal to the system that causes the change.