[QUOTE=Squink]
Still, it’s hard to beat the tiny rhyme of PV = nRT. It simply rolls off the tongue.
[/QUOTE]
You beat me to my favorite. We called it the pervert equation because once you’ve been studying long enough for you brain to start nodding off, it sort of looks like the word pervert in some fonts.
I like the equation of the normal distribution. Because it looks pretty. (not a mathematician)
A really simple one: d=rt
I had a mental block about motion problems so when it finally made sense it was a great feeling.
[QUOTE=gigi]
A really simple one: d=rt
I had a mental block about motion problems so when it finally made sense it was a great feeling.
[/QUOTE]
I learned a pretty cool trick when learning how to solve problems like this. If you arrange them in a triangle like this:
D
R T
Then, if you cover up (solve for) D, you get R*T. If you cover R, you get D/T, and if want to solve for T, you get D/R. Pretty neat, huh?
A lot of simple equations work that way. Ohm’s Law comes out as
E
I R
Where E=volts, I=amps and R=ohms
My least favorite is the Schrodinger equation. I dropped third semester Physics because of those third order partial differentials, only to have it again in graduate school.
But I digress.
Heat loss. Q=UA delta T. Wonderfull way to explain to Mrs. Plant why she should close the damn door, and turn the thermostat up or down two degrees. 
I am neither a math nor a science person. However, I’m a fan of the quadratic equation. I had to memorize the damn thing in seventh grade, and I still remember it.
The squaw on the hippopotamus is equal to the sons of the squaws on the other two hides.
[QUOTE=GargoyleWB]
I like F=ma. You could derive any physical equation or concept from that starting point. At least until that meddlesome Einstein came along…
[/QUOTE]
Our instructor used that equation to unify a graduate dynamics course - each topic became a detailed study of one term (F, m, a, and ‘=’). 
On a related note, I’ve always been partial to Kane’s Equation:
F[sub]r[/sub] + F[sub]r[/sub][sup][/sup] = 0*
Damn, I love this place!!
Only on the SDMB can you have this thread and a thread about the witches on Charmed on the same day.
[QUOTE=TwoTrouts]
The angle of the dangle is proportional to the heat of the meat.
[/QUOTE]
Actually, the angle of the dangle times the heat of the meat equals the square of the hair plus the cube of the tube.
I like pi*r^2
Cuz it’s funny.
Like, you know…pie aren’t square, pie are round.
giggle
And I like Boyle’s Law:
(V1P1)/T1 = (V2P2)/T2
i[sup]2[/sup] = j[sup]2[/sup] = k[sup]2[/sup] = ijk = -1. That and 2 + 2 = 2*2.
“What’s your favorite …?” threads belong in IMHO.
I’ll move this for you.
Cajun Man
for the SDMB
After all of my actuarial exams I became rather fond of the annuity equation:
a[sub]n[/sub]=(1-v[sup]n[/sup])/i
[QUOTE=Clothahump]
Actually, the angle of the dangle times the heat of the meat equals the square of the hair plus the cube of the tube.
[/QUOTE]
Provided that the mass of the ass stays constant.
and to be serious
y=mx+b to describe the slope of a line. Because that’s when the lights came on and I first started to understand math.
Dammit, both KJ and SpectBrain beat me to it.
My #3 fave is y = y[sub]0[/sub] + (x-x[sub]0[/sub]) (y[sub]1[/sub]-y[sub]0[/sub]) /(x[sub]1[/sub]-x[sub]0[/sub]) …a.k.a. linear interpolation.