Second Law for smart people, Entropy of a closed system cannot decrease.

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Second Law. Entropy of a closed system cannot decrease. (MIT and most everyone else).

Closed system

A closed system is a system of matter in which the matter does not change, meaning no matter enters or leaves the system. Energy can be added or removed from a closed system.

A rock orbiting the earth in vacuum is simple example of a closed system.

First Law stated for Closed Systems:

The Energy of a closed system is equal to the Energy it started with, plus the Energy Added, minus the Energy removed.

 

Does Entropy of a closed system cannot decrease make sense?

It sounds like one of those things smart people say.

The orbiting rock can get hotter when the sun shines on it (Energy added) and cooler (Energy removed) when it is in the Earth's shade. (Why?, for the same reason the Earth gets warmer in the day and cooler at night.)
An orbiting rock can get hotter and colder as a simple model of a closed system.

So plug orbiting rock into the Entropy version of second law.

An orbiting rock can get hotter and colder and the Entropy cannot decrease.

But the Entropy is the heat energy. Less Heat energy means colder.

An Orbiting Rock can get hotter and colder and cannot get colder.

Does it still sound like something smart people say?

(If you think its not fair to remove energy from a closed system, see the First Law left panel.)