Sunday, July 20, 2014

The Crow and the Pebbles - An Extension Lesson for Sink and Float

The story of the crow and the pebbles is a well known Aesop's fable. A thirsty crow comes across a pitcher of water and seeks to quench his thirst. However, there is only a small amount of water in the pitcher and its opening is quite narrow. The crow examines the situation and then uses its beak to drop one stone after the other into the pitcher to raise the water level until it is accessible to him.

I am very familiar with Aesop's fables and find them to have many scientific and mathematical elements to them, as well as social, political and economic ones. I had not thought of the crow and pebbles fable for years and then, a few months back, I came across an interesting article in the New York Times Science Section regarding it. You can view the video that was linked to the article here:

There had already been several sink and float extensions done in my classroom during the Spring months, but this narrative appealed to me and I wanted to include with it dialog about weight, volume, distribution and redistribution of mass, as well as a continuation of our on-going conversation regarding the two actions: going down and going up. Here the stones would go down and the water would go up, that is the obvious answer. However, air bubbles might be formed and those would also rise. That had happened in an earlier, outdoor sink and float work. Those bubbles were a great and satisfying surprise to all.


Photo below - The bubbles are difficult to see. They are rising on the right side of the rock that was used to secure a piece of tape and yarn. The tape and yarn were being used as part of an anchor for a student constructed boat that is not included in the photo. Wonderment is the only word I can use to describe the look on the students' faces when they noted the rising bubbles. "Air got trapped under the rock, Miss Susan, and we didn't even see it happen," one of my students told me. Ahhh...I love my role as a guide.


OK, enough digression, back to the crow and the pebble work. I also wanted to include in this work the question, "Does shape matter?" The rocks I chose for this work were pretty uniform in that they were black and somewhat flat and oval. The flexible or unstable variable was their weight, as their size varied from small to medium. I also had a box of small, smooth, colorful u-curved-shaped pieces of glass that I thought could serve to answer the question noted above, "Does shape matter?" Too, I thought they provided a little eye-candy for my students. They would therefore serve as a point of interest.

Lastly, I didn't want the water to rise with the dropping of the pebbles without something else rising with it. I wanted to include a sink and float element to the lesson. I knew I had the sink variable covered with the pebbles. I wanted the objects that were used to float upward as the water level rose to be duplicate items from the introductory sink or float work that was still on the shelf. I decided on a cork and a chestnut. The student doing the work would chose one of those items and place it at the bottom of the canning jar and then add a small amount of water to the jar to initiate the floating action. So the purpose of the work was no longer to just have the water level rise, but to bring the object to the top of the jar within the reach of the student's grasp - or, more specifically, the grasp of their held pair of tongs.

I put together a tray - actually, a small wire basket - and placed in it a blue-glass, medium sized canning jar, tongs, a sponge for clean-up, a lidded container that held within it two objects that would float (cork and chestnut), a small pitcher for water and a jar containing the colored, u-shaped glass pieces.

Next to the wire basket, when placed on the shelf, was a jar of similar  looking pebbles.  These items were placed on the shelf above the introductory sink and float work. To the left of that work is the introductory magnetic and non-magnetic work.

And then I made a goof, yup, but I went with it as I had recently read an altered version of this fable that replaced the crow with a wolf. Having recently moved from Juneau, Alaska to Madison, Wisconsin, I wrote the raven and the pebbles on the label for the stones and didn't even realize it until I placed the jar on the table in front of my students. Ravens are very common in Juneau. I explained to my students that a raven and a crow are quite similar and that both birds could use their beaks to drop the pebbles. The lesson was intact and we simply went forward.

Below - the wire basket with the items needed for the lesson and the jar of pebbles.

I removed all the items and placed them on the work mat. I returned the empty wire basket to the shelf, reserving the space for this work. One of my students filled the small pitcher with water and poured it into the jar.  I removed the cork and the chestnut from their container and placed them on the work mat, also.

I asked my students to carefully observe the water line and the fact that the chestnut was floating at that line.

I then asked another student to carefully drop a few of the pebbles into the jar. They did so.

They were completely captivated and silent as they observed that the pebbles had caused the water to rise and with it the nut.

Each student took a turn adding pebbles. 

The water level rose higher and higher.

A student then used the tongs to remove the chestnut.

All immediately asked to repeat the work and we did. 

After the second time doing the work with the pebbles, I opened the jar with the u-shaped glass pieces and asked the question, "Does shape matter?" They asked back, "Does a pebble weigh the same as one of the glass pieces?" And, "If the glass doesn't weigh as much, will it take more of them to make the water rise?" I invited them to compare one of each and discover any weight variances.

The photo below illustrates that comparison work. Here one of the students holds one of each object on the very edge of her fingertips and compares the weight of both. This is exactly the way students hold the baric tablets to compare variances in weight and to find those that match. The glass pieces did weigh noticeable less.

They repeated the lesson exactly as they had done with the pebbles.

We sat back from the table after the work was completed and talked about water displacement, about how the locks work on the Erie Canal and about how weight has force and that force can be used as leverage.

Each of my students contributed ideas and insights. Then one of my five year olds looked at me and said excitedly, "Miss Susan, I know. It's like when you take a bath. The water rises when you sit down in it. The water has to go somewhere, so it goes up. Well, if there was a hose attached to the tub to let the water out when it rose, then it would go out the hose." Another student jumped in the conversation and said, "I think that has something to do with water pressure. The water has weight and it forces itself to find a way to get out of something when it doesn't have room." A third student stood up and said, "If you bring your foot down hard in a puddle, the water splashes." He then demonstrated the act of stomping in water. Right then, the head of my school walked in and said parents were waiting and that my students needed to pack up quick to go home. Ahhhh...but it was wonderful.

I repeated the above lesson only with the label on the stones amended to correctly read, "The Crow and the Pebbles," during the first week of summer camp here at Toad Hill. Again it was amazingly successful. This time several of my younger students engaged the work. They had not when it was first presented in the classroom. Here are a few photos of the work being done outside:

With pebbles...

With u-shaped, glass pieces...

Interestingly, when we came in to get out of the sun for a little bit, my youngest students immediately took the introductory sink and float tray off the shelf, they had already had a lesson or two on it, and went to work. All good - so very good!

There is still something tugging at me about this work, though...beaks and their size and shape. What is the span of an opened crow's beak compared to a robin's? What is the the geometry of a bird's beak? Triangular when opened, cone shaped when closed? How much weight can a crow lift with it's beak and how can a child visualize a beak as a tool? What tools are they familiar with that resemble and are used similarly as a bird's beak? I have a hundred more inquisitive questions. In the classroom, the children ask the questions after I have provided materials and lessons that provoke curious ideas and insights within them. Here, is where I ask questions. More just popped into my head...better call it a night. Hey, it's raining out. Maybe I will go and stomp in some puddles and try to measure the arc of the spray of water. Wonderment. I have it too!

View a post I wrote about Sink and Float a few years ago here: