This is not a homework question but what I thought was a typo in my textbook.
I see that propane will boil off at -40F (-40C)
Do you see what I see?
What gives?
Instructor scratched his head and told me to just let it go as I’ll not NEED to know this out in the field.
That happens to be the one point on the scale wherefahrenheit and celsius scales match.
What, -40 C = -40 F? That’s where the two temperature scales cross. Yes, they represent the same temperature. Or is it something else that I’m missing?
No. you’re good to go.I’m the one missing something and that’s why I asked.
Also, I use 1.8 instead of 5/9 to do the maths. Is that gonna mess me up?
Well 9/5 = 1.8 so as long as you are converting C to F, you are OK.
I’ve been subtracting 32 then dividing by 1.8 to convert F to C.
That’s correct.
You can always check the formula by plugging in the boiling point of water - 212°F, 100C
212-32 = 180
180/1.8 = 100
Check.
I much prefer this method:
Add 40
Multiply by 5/9 (for °F to °C), or 9/5 (for °C to °F)
Subtract 40
For a quick approximation, subtract 32, divide by 2, and add 10%.
Here’s an example : 100F
100-32 = 68, 68/2= 34, 10% more = 34 + 3.4 = 37.4 C
This is just a simple Mclaurin series expansion - and is very easy to remember and do the math in your head. Here’s the Explanation
C = (F-32)/1.8 = (F-32)/(2x(1-0.1))= (F-32)x(1+0.1)/2 — approximating to first term of the mclaurin series
From what I understand this formula is used for weather conditions.
I figured that out when I lived in Mali, where temperatures are delivered in Celsius. People were amazed that I could convert it in my head, until I pointed out that you really don’t need to use 1.8 unless you’re working in the sciences. I was a little sloppier with it, though. If it was 40C, I’d double it, add 30 and knock off about 5 degrees; so 105F. Close enough.
All the formulas everyone is quoting are equivalent. Some are the fully accurate version and some are approximations good enough for mental math.
All these formulas work on anything measured in Fahrenheit or Celsius. Doesn’t
matter if you’re taking the temperature of propane, molten lava, weather, a martini, or your baby’s rectum. No matter the substance or circumstance, degrees F is degrees F and degrees C is degrees C. F = C * 1.8 + 32 or C = (F - 32) / 1.8 always works.
And to loop back to the OP … if you plug -40 into either formula, -40 pops out the other side.
That you teacher did not know -40F is -40C makes me question him. I forget this fact over the years (and I have had a few) but when ever it comes up it is like oh ya that’s right.
He knew, and was proud that I took it upon myself to find the answer.
Sometimes we learn through embarrassment, I guess.
Now I’ll never forget this bit of info.
Thanks all.