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 | , , , | 8 Comments