MR BUNN’S FIRST LESSON – USING A McMORRAN BALANCE TO DETERMINE YARDAGE

Some people have asked how Elder Daughter (about to be 15) did all the math that led up to her bunny’s pirate sweater.  I don’t think they were asking how she was able to accomplish the task in the first place, but instead, what methods she used.  All those numbers sound daunting, but it’s really not that hard if you take it step by step.  I wanted to to do as many steps as possible, so we started out with as little information beforehand.  Here’s what she did, taken in large part from the write-up that was on her poster.

First, as I said – I was evil.  I gave her a lump of yarn without a label.

Now I knew what it was, but Evil OverMoms don’t tell.  The first thing she did was determine how many yards of yarn she had.  Here’s her write-up (the spacing on the equations is a bit squirrely because they were exported from MS Word’s equation editor):

First, I had to find the total weight of the yarn. Using a scale, I found I had to 225 grams of yarn, total.

Then, I turned to a precision instrument to help me. The McMorran balance is designed to determine yardage per pound.  The formula that comes with the balance requires the user to first find out how long a piece of yarn is needed to make the balance register level.  My balancing length for this yarn was 9.75 inches.


 The next step is to use the formula that comes with the balance to determine yards per pound (YPP):

 

 In my case

My yarn has 975 yards per pound, but I needed to find out how many yards were in 225 grams.  The formula to convert grams to pound is:

Plugging in my values I find out:

Now I multiply YPP times my weight in pounds:

And so Elder Daughter defeated the first yarn demon, and determined how much yardage was contained in her tangle – a whopping 482.6 yards.   I’ll post more in this series when she brings her poster home and we can scan her drawings.  For the record, McMorran Balances also come in a metric version.  But I have the Imperial unit one, and it was more fun to make sure she did as many conversions back and forth as possible.  

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