Kids learn by example, and teaching science concepts such as density can be accomplished with fun classroom activities. Everything is made up of molecules. Density is the measure of how tightly the molecules are packed together in the solid object, liquid or gas. With some materials, such as liquids and gases, the density can be changed. With solid objects, the density cant be changed.
Gather materials needed for the density experiment. A large glass container, such as a glass bowl or small fish aquarium, or a couple of glass jars will work fine. Additionally, other objects, such as a hard-boiled egg, a fresh egg, a tennis ball, wine corks, grapes, 1 cup of salt and limes or lemons will be needed.2
Discuss with students how everything has a density. Make a list of all the materials that will be tested for the experiment on the front board. Allow students to guess if the objects will sink or float. Write guesses next to the objects on the front board.3
Fill the container with plain tap water. Because the density of water is low, objects that have a higher density will sink, and those with a lower density than water will float. Gently place each object for the experiment in the water except for the salt, and take note if the objects sink or float. Do any of the objects have surprising results?4
Remove all the objects from the water, and discuss how the density of the water could be changed. When objects are heated, cooled or changed in other ways, the density can be affected.5
Add the salt to the water, and mix well. Discuss with students if the salt being added to the water will change the density of the water. Do students feel it will change how the objects will behave when added to the water?6
Gently add the objects to the salt water one at a time, and observe the reaction. Do any of the objects that had previously sunk now float? Write the observations on the front board.