Playing in water opens many avenues for science explorations—flow, wetness or phases of matter, volume, and buoyancy. Unexpected results make children think and explore further. For example, children know that fish are supposed to float, so playing with a toy fish that sinks will get children thinking about why. We can let children know that questions are to be shared by listening to theirs, asking open-ended questions, and then having the students record their answers, or dictate to us to record. Science activities are good platforms for using literacy skills because children often want to tell the story of what they did. Read the November 2009 Early Years column in Science and Children about creating a book about a classroom investigation. View sample book pages at www.nsta.org/SC0911.
Given an assortment of interesting objects and a tub of water, children will make discoveries while playing. Demonstrate the definitions for those unfamiliar with the words “float” and “sink” with two objects, perhaps a cork and a coin. With experience and enough interestingly shaped objects, students learn that whether an object floats or sinks is related to both the material it is made from, and its shape. To begin with, a sink-or-float exploration can focus on the property of materials. Materials which challenge assumptions include, sponges, pumice, fruit, small lidded containers (some completely, some partly, filled with water), soap, and dense plastic models of animals that swim (children often think these will float like their real-life counterparts). A variety of balls, jar and bottle lids, keys and coins, plasticine clay, and sea shells are attractive to children, and they may also want to choose items to test from the classroom.
After a period of minutes or days of exploration, students can do some predicting using this knowledge. Using exaggerated body gestures to represent our predictions is fun. “Do you think it will float?” Put your hands high above your head and gently wave them like they are floating above you. “Do you think it will sink?” Slide your hands down from your shoulders to your lap like they are sinking. With a bit of direction by the teacher towards documenting their thinking in drawings or writing, the children will have a record of their predictions to compare with what they find out when they put the object in water.
Students can explore buoyancy with a Discovery Bottle—for details read Sandy Watson’s article, Discovery Bottles, in the July 2008 issue of Science and Children. She explains how “Discovery bottles are inexpensive, quick to assemble, and an excellent way to provide students with practice in developing science-process skills, such as observing, measuring, predicting, and so on.”
The next time you can present some new objects and ask the children to separate the objects into groups, those that they think will float and those that they think will sink. The children may choose to create a third group of those objects they aren’t sure about, or objects that sometimes sink and sometimes float. Be sure to let children know that it is okay to have differing predictions. To keep the two concepts clear in their minds, use two clear cups on the table, one with a sinking object in it and one with a floating object in it, to represent the two groups, and the children can place objects around the cups. Tell the children that scientists ask questions and try to answer them and they can too.
I like to keep some towels handy to help with clean up, and to rinse all objects with a bleach solution and allow them to air dry before storing. Send home the children’s papers documenting their work  and it might inspire families to continue the exploration at home in the bathtub or at the sink.
Peggy