Select Page

by Beth Bailey and Meredith Cavallaro, Primary faculty 

One of our Primary classes started a new unit, sink and float, this fall. This particular exploration involved the scientific skills of prediction, observation, and investigation (to name just a few). Things kicked off when students were amazed to find their pumpkins floated and didn’t sink as many expected. Curiosity aroused, the class decided to investigate more about what makes things sink and float.

First of all, the class took time to observe whether or not a variety of items would sink or float, including: paper clips, pencils, corks, plastic spoons, metal spoons, corks, sponges, and legos. They made predictions about what might happen, then placed each item in the water to see if they were correct. Students also recorded what actually happened with each prediction.

This led to many discussions about what was observed, leading to a the central question, What made some items float while others sank? The focus, at first, was on an object’s weight. However, the class noticed heavy items can sometimes float and light items can sometimes sink and the material an item is made of can sometimes help predict what it will do, but not always. It was very difficult to find a pattern or rule that would let students make an accurate prediction.

Sink and float testing

Density, Predicting, and Investigating

The next few days allowed for independent investigations during settling in and choices time so the children could experiment with different materials and shapes to see if they would sink or float.

Next the class began looking at items that have similar properties. We tested 3 cubes made of different materials (sponge, wood, metal) and two different types of rock (pumice and granite) to see whether they would sink or float. Some of the results were not what we predicted. As the class worked, they recorded the data in different ways. For this investigation they created a chart, then colored and cut out pictures of the items tested to put on a big poster. The variety of skills they are learning—and honing—includes: observation, classification, predicting, investigating, charting, and graphing.

They also investigated plastic toy animals but soon discovered the type of plastic was not consistent.  Some were solid plastic and others were hollow. This led to new observations: a rubber duck was able to float but kept tipping over, an octopus and a fish had air pockets and by placing them in the water in different ways the class was able to, sometimes, impact the object’s floating abilities.

Children are being exposed to the idea of density; although they are using different language to describe the differences at this point. In their observations they noticed plastic items would float; but then realized the shape or the “hardness” of the plastic impacts if it floats or not. Having a space for air—an air pocket—makes a big difference in an object’s ability to float. They are also realizing the shape of something and the material its made of plays a part as well.

The children all tried this at home and brought in their item along with their prediction and findings to share with the class.  

How to Make Clay Float

As the unit drew to a close, the class was challenged to figure out how to make a cube of clay float. First they tried rolling it into a ball—it sank. They flattened it—it still sank. Then we added a “dent” to try and create an air pocket since we had observed objects with air pockets floated. The children suggested making it thinner and by making the right shape the class discovered they could make a material that originally sank into one that would float!

Once the class knew it was possible, the children were each given a brick of clay to form into a vessel of their own. They used their strong fingers to work the modeling clay into float-able vessels. It took a lot of work to get it thin enough and just the right shape to get it to float. Many friends tried multiple times, making adjustments before their vessel was a floater.

After the clay was able to float, testing began to see how reliable it was. We tried adding pennies to our clay vessels to see how many they would hold before they sank.

The sink and float unit continued as the students investigated how well differently shaped vessels float. The class chose a few different vessels, made of styrofoam or plastic, that appeared to float well to see how much they could hold without taking on water or sinking. Students noticed that the way the items are placed into the vessel has an impact on how much it will hold before it takes on water. After experimenting as a large group, the children worked in small groups. Some groups had very different results depending how they added items to the vessel. They started to notice that a vessel will hold more if the items it carries are distributed evenly. Stacking items in one area made the vessels tip over quickly.

From honing predictive abilities, to utilizing fine motor skills, to understanding the concept of density, sink and float, is an example of hands-on learning at its best.