Thank you, Jeff. Yes,
Thank you, Jeff. Yes, measurement and calculation is what I am finally seeing it is all about (not philosophical whims and rhetorical fancy).

(I hear you about the CAPTCHA. I’m worried it’s going to break out into finding derivatives and I’m going to have to search my shelves for an old textbook.)

I see … I did read Part 1
I see … I did read Part 1 and maybe I was drawn into the reference to Colding and a mechanical equivalent to heat, and thinking “ok, shouldn’t start with a base case of discussing *energy* before we start in on the specifics of one type (thermal)” … but now see from your explanation that as a law specifically applied to thermodynamics, we need to start with a system that allows us to measure that specific kind of energy, and on that basis the order is starting to make more sense … Ok now, forgive my continued exploration, just that the word “energy” (not “heat”) in the first law piqued my attention: Does the first law really apply to all energy – kinetic and potential? … or just all kinetic? (thermal, mechanical, magnetic, etc.)? … or some subest of kinetic only? … I do see the corelations between mechanical and thermal energy, and apperciate your examples of engines and ceiling fans and such. But wondering how far the first law can be extended to evaluate (eg. sniff out scams) in new systems using magnetic or chemical or sound energy. In my position, marketing folks and entrepreneurs throw out all kinds of crazy claims, the verasity of which is mostly easy to identify, but not always … this is the reason for my asking; not sure if it needs to be answered here. Love your articles (and the commments of your community), Allison … always stimulating.

Simply: we have already said
Simply: we have already said there is equilibrium between the ice and the cold air in the freezer. Let’s say there is also equilibrium between the ice and the ice tray. The zeroth law tells us that ice tray and the cold air of the freezer are also at equilibrium. They use the same scale to measure the temperature. This one law allows even mere scientists AND engineers to make important calculations.

-Neither a scientist, nor an engineer (and why do the numbers in the CAPTCHA keep going up as I keep commenting on this article?)

Great question, Clay. The

Great question, Clay. The answer lies in what I wrote about temperature above. The first and second laws lean heavily on temperature. If you read the second article in this series (part 1), you’ll see that I talked about how the technical form of the first law is a relation between work, heat, and internal energy. You can’t quantify heat without a way to measure temperature. The zeroth law basically defines temperature and thermometry.

I guess that no one else
I guess that no one else wants to take on this question. If you assume that air in a duct is an ideal gas (which is a very good assumption), then the temperature does not change. Conservation of energy says that the fluid enthalpy does not change since there is no energy (heat or work) exchanged with the surroundings, and enthalpy is only a function of temperature, not pressure, for an ideal gas, so the temperature does not change. If you really want to get into the details, if you have a large enough pressure drop in this adiabatic duct, you might get a detectable temperature change, but it will be a decrease, not an increase.