Sink or Float: Teacher's Activities

Many children wonder why some things sink and others float.Jupiterimages/Comstock/Getty Images

Children are often entranced by the concept of floating and sinking. Even toddlers can play with this concept in the bath or the swimming pool, but preschoolers and grade schoolers enjoy exploring it to try to understand it better. As a teacher, you can present activities to your class that encourage them to explore the concept further.

Basic Preschool Activity

Preschoolers do not yet fully understand the concept of sinking and floating, and they may think that anything "big" or "heavy" will sink. To help them experiment with sinking and floating objects, gather several small objects from around the house, such as a washer, a sponge, a plastic cup, a toothpick, and a pebble. Ask children to predict which objects will float and which will sink. Then, let your pupils take turns trying them out, placing them into a basin of water and seeing whether their predictions were correct. Discuss the fact that some small, seemingly light things, such as a washer or pebble, sink, whereas some larger things, such as a sponge, float.

Most objects either sink or float, but you can boggle students' minds with raisins that seem to do both. To prepare this activity, you will need to fill a large container with vinegar and water in a 3:1 ratio. Then, slowly add two teaspoons of baking soda to create carbonation. When you drop raisins into this mixture, they will seem to sink to the bottom, but then come up to the surface again. You can explain to students that the carbon dioxide bubbles in the mixture attach themselves to the raisins and lift them to the surface. You can try this with other small objects, such as grains of rice, popcorn kernels, or small chunks of fruit to see how the results differ.

Your students can have fun working in groups to figure out various ways that they can sink a paper boat. Each group of students should receive a paper boat that they can float in part of a large basin. The students should then take turns trying to come up with ways that they can sink the boat. The most obvious way, of course, is to add some weight to the boat by filling it with pennies or other small objects. Your students will eventually realize that tipping the boat so that it is filled with water can also help it sink, and poking a hole in the bottom of the boat can make it sink as well.