Sink and float activities introduce kids to the basic scientific principals of density and water displacement. Since these concepts are taught in every elementary grade, vary the difficulty level according to the age of the students. Younger kids may simply test which objects sink and which ones float. Older kids can experiment by changing the variables involved in sinking and floating, then recording the results.
Sink and Float Activities
The Great Schools website recommends creating a chart with three columns labeled "Objects," "Predictions" and "Outcomes." Provide children with a tub of water and several objects of different shapes, sizes and weights. Record the name of each object on the chart and ask the children whether they think each one will sink or float. Write the kids' predictions on the chart, then have them drop the objects into the water. Record the results of the experiment on the chart and compare them to the predictions.
Water Displacement Activities
According to the BrainPOP Jr. website, objects will float if they weigh less than the water they displace or move out of the way. Objects that weigh more than the water they displace will sink. Children can experiment with water displacement by comparing boats made from a variety of materials. Give groups of children cloth, craft sticks, clay, paper and other materials with which to build a boat. The kids can gently add the boats to a tub of water and observe which boats sink and which ones float on the surface. As a group, create a chart with columns labeled "Sink" and "Float." Record the type of material from which each boat was made in the appropriate column, then discuss the weight of each boat relative to the weight of the water it displaced.
Comparing Types of Water
Children already familiar with basic sink and float experiments can investigate the effects of different types of water. Have the kids drop objects into tubs alternately filled with fresh water, salt water and carbonated water. Label a four-column chart with the name of each object down the left side of the chart and the types of water across the top of the chart. Record each object's ability to sink or float in each kind of water.
Guide students to discover the fact that the air bubbles in the carbonated water make it less dense than fresh water, while the salt in the salt water makes it more dense than fresh water. Discuss how the density of the water affects the amount of water an object will displace.