[Diy_efi] OT - Measuring less than an ounce

[Daniel Nicoson]

I hope you guys don't mind this totally Off Topic, but you are one of my
more scientific group of friends.

I need somebody to review my physics/methodology below:

Helping my daughter (16 yr old) with a science project.  She is testing two
types of fertilizer by growing three equal size patches of grass, fertilizer
A, fertilizer B, Control.

Here's the real problem:  We need to measure VERY small amounts of granular
fertilizer.  The grass patches are only .38 ft^2, one fertilizer amount
comes out to .0213 ounces, the second comes out to .24 ounces.

I don't know about you but I don't have that kind of scale around here.

Here's my idea, please scrutinize, simplify, accurize...

I am going to weigh 300 pennies tomorrow at work on an electronic postal
scale, I think it reads out in 10ths of ounces.  If they read greater than 1
ounce I should get 2 significant digits, possibly they will weigh more than
10 ounces and we can work with 3 significant digits.  The assumption is that
the pennies all weigh the same.  This will give me an accurate weight of one
penny.

Back home this weekend we will make a simple balance beam.  Since I don't
have jeweled bearings, I'm thinking a simple string at the fulcrum will give
as consistent results as anything.

At the short end, say 10-to-1 ratio of lengths, I will have a hanging
container with pennies.  At the other end I will have a plastic medicine
bottle to hold the fertilizer.

To zero the balance scale out I will add coins (any size) until the coins
balance out the whole apparatus.

Next, I will have to do the math as to how many pennies equal 10 times the
weight of the desired fertilizer weight.  Place this measured amount of
weight in pennies on the short end of the balance.  Next, fill the medicine
bottle with fertilizer until it balances.

Done, measured, accurate weight of fertilizer.

Does all of that make sense?  It does to me.

The hardest part will be helping her learn what we just did so she can
defend her process on the project.

Suggestions are appreciated.

Dan Nicoson