# Talk:2566: Decorative Constants

I don't have any idea what to put in the actual description, but whoever does should probably note that r(in) - r(out) equals zero, not one. And multiplying by a constant 0 absolutely changes the value! GreatWyrmGold (talk) 21:59, 10 January 2022 (UTC)

- r
_{out}and r_{in}are different values. The subscripts represent different instances of the same variable at different point. In the same way, you might calculate something happening over a time interval t_{end}- t_{start}. 172.69.71.77 23:02, 10 January 2022 (UTC)- Yes for sure they are two different values. On the other hand if μ is not 1 then the it is not just decorative! D on the other hand is just a proportionality constant, which may have a value other than 1. I have tried to put something in the explanation here. Quite a bit. Do not really now anything about Drag, so just took it from the wiki page. Also I hope someone can explain the formula in the image, as I'm sure it is just something about the flow, that would relate it to a drag equation. --Kynde (talk) 23:41, 10 January 2022 (UTC)

Note that the title text is pretty much word-for-word a repeat from Randall's book *How To*. In Chapter 11: *How to Play Football*, he misuses the drag equation, and mentions this fact in more depth, in a footnote. Bit of trivia! --162.158.134.79 23:13, 10 January 2022 (UTC)

- Nice, I will have to check up on that. Thanks. --Kynde (talk) 23:41, 10 January 2022 (UTC)
- Can confirm this, the book mentions that the "traditional tribute to Euler and Bernoulli" comes from Frank White's
*Fluid Mechanics*textbook. Clam (talk) 01:08, 11 January 2022 (UTC)- There it is, page 266 in the 1986 2nd edition: "They both have a factor ½ as a traditional tribute to Bernoulli and Euler, and both are based on the projected area..." https://books.google.com/books?id=wGweAQAAIAAJ&q=traditional -- 172.70.162.5 02:13, 11 January 2022 (UTC)

- Wait, wouldn't the values be twice as big (rather than half as big) if you left off the 1/2? 141.101.69.154 12:43, 11 January 2022 (UTC)

Of course, the c^2 im e=mc^2 is just as decorative, when using natural units where c=1.... 172.68.50.171 00:29, 11 January 2022 (UTC)

- And the resulting equation is then just e=m - or m=e which is beautiful and profound. "Mass is Energy". Without the complications, you stop thinking of it as a PROCESS for converting one into the other and get the more profound point that Mass and Energy are the exact same thing. SteveBaker (talk) 03:33, 11 January 2022 (UTC)
- I respectfully disagree. The c² isn't decorative; mc² is a measure of energy and m is not. e=mc², like f=ma, still works even if you change the size of any of the basic units (of length, time, mass) from which the units of energy and force are derived. As I see it, an equation that ties you to any definition of unit size is less profound, not more. Tom239 (talk) 17:21, 12 January 2022 (UTC)

I think the 1/2 in the drag equation is intuitive. I understand that it is technically superfluous, but F=Pd*A and Pd=1/2*rho*u^2 so the 1/2 carries over intuitively. 172.70.98.15 (talk) *(please sign your comments with ~~~~)*

- Agrees I had this written down in an early version of the explanation but that was edited out. Maybe I will put it in again.--Kynde (talk) 10:44, 12 January 2022 (UTC)

Drag coefficients could just as easily be half as big. This is true but how is their being unitless relevant? It's more about how defining constants is partially arbitrary. Lev (talk) 08:07, 12 January 2022 (UTC)

- If Cd had a unit, say it was an energy which represented some relevant value for a given material, then it would not be correct to say that it was half as much, just because 1/2 came into the equation. But if it has no units, then it is just a constant saying something about the material, and then the 1/2 could in principle be absorbed without changing anything. But as stated above 1/2 actually has physical meaning in the way it enters the equation. --Kynde (talk) 10:44, 12 January 2022 (UTC)

- It doesn't make any difference. For instance, Coulomb's law works fine whether we write it F = -q
_{1}q_{2}/(4πε_{0}r^{2}) or F = -kq_{1}q_{2}/r^{2}. Similarly, if we had a factor of 2 in the gas law for some reason, that would just change the values of the gas constants.

I've seen the double-struck capital "D" used commonly as a symbol for the Domain of a function (While the double-struck "R" was used for the range in that context) 162.158.63.243 21:16, 17 January 2022 (UTC)

Does anybody know enough math to figure out what that equation is supposed to do? I really want to delete that tag.New editor (talk) 19:13, 25 January 2022 (UTC)

- The r terms are used in describing things like water treatment plants or dialysis machines, where you're trying to use fluid flow to regulate some solute. If fluid balance is large, it means the "tank" is going to empty or dry out. I guess T is the rate at which this happens. Not really a math thing, more of an engineering thing, seems to me.

## Count down clock

See Countdown in header text. Discussion has been moved here Talk:Countdown_in_header_text. --Kynde (talk) 11:10, 12 January 2022 (UTC)