Check out Steve Mould's Pythagorean Siphon video:    • The Pythagorean Siphon Inside Your Wa...  

Every Pi Day I calculate the digits of π somehow. This year I counted the number of molecules in a disc as a 'real accurate' way to measure its surface area. You can see all the previous videos here:    • Calculating π by hand the Isaac Newto...  

Yes, you can buy the sheets of paper I wrote on in this video. I've signed them and all money goes to WaterAid UK. https://www.ebay.co.uk/usr/standupmaths

Here is the calculation (keeping mL and cm units throughout).

Our 7 drops were 0.1 mL of solution which is 0.00005 concentration.
Oleic acid is 282.47 g/mol and 0.895 g/mL.
Using Avogadro's number of 6.02214 × 10^23 that is 9.54 × 10^15 molecules of oleic acid.
That is a volume of 5.24081 × 10^22 mL per molecule.
Which is a length of 8.06243 × 10^8 cm and area of 6.50028 × 10^15 cm^2.
Total area of 62.016 cm^2.
The disc of molecules had a radius of 4.000 cm and so that gives us π = 3.876 (I lost 0.001 because I was rounding as I went).

CORRECTIONS:
No, I didn’t publish early by accident! I try to put πDay videos out a bit early so teachers have time to use in lessons before/on π Day.
I’m hearing reports that oleic acid is not an oil, the carboxylate end makes it a surfactant (first mentioned Ian Roberts). I blame any and all chemistry mistakes on Steve.
Let me know if you spot any other mistakes!

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Filming by Matt Parker and Steve Mould
Editing by Alex GennBash
Music by Howard Carter
Design by Simon Wright and Adam Robinson

MATT PARKER: Standup Mathematician
Website: http://standupmaths.com/
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