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Comment by ainoobler | Hacker News Reader

Fundamentally, yes. All motion does end up adding entropy to the environment. This is especially egregious for fossil fuels which are literally combusted/oxidized to move chunks of metal on wheels carrying different kinds of cargo. Electric vehicles change the dynamics somewhat but the motion of magnets still ends up contributing entropy to the environment at a somewhat reduced rate than fossil fuel vehicles.

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Heat and entropy are different concepts. Also, motion can reduce entropy locally, even if globally it always increases. For example, when a puddle freezes, the puddle's entropy goes way down. The entire Earth's entropy can also go down, as long as the entropy of the universe increases.

How are heat and entropy different?

Heat is energy that causes something to raise in temperature, and is measured in Joules. Entropy is a harder to pin down concept, related to the internal state of a system, and is measured in Joules/kelvin. In certain processes, the change in entropy is equal to the change in heat divided by the temperature of the system.

Sounds like it's the same thing.

It is not. Two bodies can have different entropy even if they are emitting the same amount of heat.

Where are the calculations?

dS = dQ / T

So T = dQ/dS. Seems like the same thing.

If they were the same thing, then T=1. Since there are many many bodies with T != 1, it follows that dQ is rarely equal to dS.

They are closely related but not the same. DeltaS = DeltaQ /T

A lot of it comes down to whether a process is reversible or not. I've taken multiple courses on thermodynamics and still only understand it a little.

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