antripathy

When a train moves it hits the air which in turn gets energized and converts to wind.This energized air becomes so due to transfer of energy from the moving train.This can be felt so obviously if one stands a little close to the side of a fast moving train.This train made wind can produce(partially) potential electric energy by installing suitable size wind turbine generators on both sides of the railway track.

To know the reply it must be found out how they were separated in the first place.

In case of 100% reversibility a perpetual machine becomes,in theory,possible.In case of partial reversibility it can lead to energy efficiency in the sense that a part of the same energy can be used again.

The question is about reversibility,2nd law assumes it is absolutely not reversible. The rocket energy that hurls the satellite in to space becomes partially reversible on return path to earth.

When a man made satellite falls towards earth its energy can be collected by fixing a wind turbine generator above or below it.It is so obvious but how does 2nd law of thermodynamics explain it.

Work can be done when energy flows from high temperature or potential area to lower one even if the quantity of energy is small,say 25 joules.No work can be done when it is in equilibrium, that is uniform temperature and pressure.The atmosphere and oceans contain trillions of joules of energy,brought down from higher temperatures and useless for doing the daily works of the humans.