It’s Not All Mary Poppins

Science made simple

We made chocolate chip peanut butter cookies this morning.

“Why are you putting the peanut butter in the water, Mary?”

“It’s the best way to measure it. I need one cup of peanut butter. Problem is, peanut butter is very thick. If I were to push the peanut butter into the measuring cup, I wouldn’t know if there was an air bubble in there, right? I wouldn’t know that I was getting exactly one cup of peanut butter.”

“Why are you putting the peanut butter in the water, Mary?”

“Well, let’s start over.” I dump the water out, and set the peanut butter on a plate. “We’ll put one cup of water in the measuring cup. See? Right up to that line.”

“The line with the number one?”

“Good for you, Emily. Yes. Now how much water is in there?”

“One cup.”

“That’s right. Now watch what happens when we put in the peanut butter.” I let each child take turns dropping in a spoonful of peanut butter, and we watch the water level rise. “Okay, now where is the water?”

“At the two!” It’s a good thing one of them can read her numbers…

“So now the water has moved up, from one to two…” and suddenly I am faced with the realization that these kids do not yet have any concept of conservation of mass or volume. If you fill a tall skinny glass and a short fat glass with the exact same amount of water, water which they saw you measure, they will swear up and down the tall skinny glass has more in it. And will fight to drink from it.

Some — but not all — of them understand the concepts of “more than” and “less than” but even those who get that much have only the vaguest of notions that “two” is “one more than” one. This is sophisticated stuff.

Ummmm… Four pairs of eyes gaze at me and stare at our peanut butter, still in its bath. I’m stalled. What I need is a total change of approach. Off goes Normal, Soft-Spoken Mary, and in comes Bright and Cheesy Mary.

“You know what?? This is called ‘Archimedes’ Principle’!!! Can you say ‘Archimedes’?”

“Ar-ka-mee-deez!” They like this game. They’re not sure who Bright and Cheesy Mary is, but she’s sure is entertaining!

“That’s right! Archimedes is someone’s name. He was a man who lived a long, long time ago. He was a very smart man. A very smart man who discovered that you could measure peanut butter by dropping it in water!!”


“That’s right. Let’s all say it again!”

And we do. And then we mix the peanut butter with the butter and beat in some sugar and eggs, and get on with the business of making cookies. Which is really what we came to do, anyway.

Archimedes can wait, just a bit…

July 22, 2010 - Posted by | random and odd | , , ,


  1. I can’t help but think of the Archimedes death ray episode of Mythbusters when I read this.

    Totally, absolutely never in my life heard of Mythbusters.

    Comment by Bethany | July 22, 2010 | Reply

  2. I remember that episode!

    And I have to say that THIS is brilliant and WILL be used for peanut butter measuring in our house in the future.

    My grandmother taught me. It’s one of those grandmotherly things. She also taught me what I know of sewing, too, pretty much.

    Comment by Bridgett | July 22, 2010 | Reply

  3. So cool! I’ve used it for shortening but it never occurred to me to try it with pb. I usually just spray the cup and hope for the best.

    Spray the cup? With peanut butter?

    Comment by jwg | July 22, 2010 | Reply

    • pam(baking spray)

      Comment by jwg | July 23, 2010 | Reply

  4. Their parents are going to be gob-smacked when they talk about Ar-ka-mee-deez.


    I’m rather hoping so!

    Comment by surya | July 23, 2010 | Reply

  5. oh, wow! i never thought of measuring peanut butter that way! but, as we have nut allergies here, i will probably promptly forget this cool trick!

    It’s not just works for peanut butter, but will work with anything solid (and solid-ish) that isn’t water-soluble. So… butter, shortening, margerine.

    Comment by Dana | July 23, 2010 | Reply

  6. That has seriously never occurred to me. I’m in awe.

    You can thank my gran, who taught me. I’m sure she was taught this in school, as girls were back then. Some skills and tricks truly are timeless!

    Comment by Sylvia | July 23, 2010 | Reply

  7. Wow….You rock! I can’t wait to show my kids this trick. And how can you not have seen Mythbusters? Clearly you do not have a houseful of science geeks, like I do.

    All credit goes to my grandmother. (I hope she’s hearing this, wherever she is…)

    Re: Mythbusters. Perhaps it is the age of my geeks? Back when my kids were watching television, we were avid fans of Bill Nye the Science Guy. None of my kids really watches television any more, though, and I never do, so if it’s newer, we’ll have missed it.

    But to prove our science geek-ness, my youngest just came back from visiting her older sister for a week, TOTALLY psyched about the birthday gift she got. “The best birthday gift, ever, mum!!” What was it? A life-size model of a skull. “Look! The jaw hinges! And see? You can lift the top, and see what the inside of your head would look like if there was no brain in there! Is that not the coolest? And now I can learn the NAMES of all those bumps and things!!!”

    Oh, and the skull’s name? Yorick. What else? 😀

    Comment by Tammy | July 23, 2010 | Reply

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