Prior to conducting the experiment, students should conduct some background research into the concepts of density and buoyancy. Students should have a basic understanding of what density and buoyancy are and how they operate; this will help them to develop a hypothesis about whether the egg will float in the saltwater. After the students have conducted their research and developed a hypothesis, they will need to gather their materials, as well as a journal and a camera to record their results. In order to conduct this experiment, students will need one egg, water, salt and a tall drinking glass.
Students should begin by filling one glass almost full of regular tap water. Students should gently put the egg into the water, and record what happens to the egg by taking pictures or making notes in their journals. Then, using the spoon, students should carefully retrieve the egg from the glass. Pour approximately 10 tablespoons of salt into the glass and stir. Students should again gently lower the egg into the water and record the results. The egg should sink in the plain tap water and float in the saltwater.
In a similar experiment using the same materials, students can use saltwater and fresh water at the same time to demonstrate how an egg will float in saltwater. Students should begin by filling the glass about half-full with fresh water and stirring in about 7 tablespoons of salt. Then they should slowly pour in fresh water until the glass is full. Students must pour slowly in order to avoid mixing the saltwater with the fresh water. Using the spoon, students should then lower the egg into the water. The eggs should sink through the fresh water and then float suspended in the glass when it reaches the saltwater.
In both sets of procedures, adding salt to the water increases the overall density of the fresh water. After completing this experiment, students should understand that objects are buoyant (meaning they will float) if the object has a lower density than the liquid it is immersed in. In this case, an egg is denser than fresh water, so it sinks. However, by adding the salt and increasing the overall density of the water, the water becomes denser than the egg. Thus, the egg will float in the saltwater. In the second set of procedures, the egg will suspend in the middle of the glass because its density is higher than the fresh water on top of the glass but lower than the density of the saltwater in the bottom of the glass.