This activity will help your child understand the concept of density and learn why objects sink or float.
- 2 clear drinking glasses
- 2 eggs
- Fill one glass half-full of water.
- Mark the water level on the glass.
- Add salt a spoonful at a time and stir it into the water until it dissolves. Stop adding salt when it won't dissolve anymore.
- Notice what happens to the water level as you add salt. The level shouldn't rise; instead, the water gets denser as it becomes saturated with salt. When you dissolve salt in water, you cram more molecules into the water without making the water take up any more space.
- Fill the other glass half-full of plain water. Gently put an egg in each glass. The egg in the saltwater should float, and the egg in the freshwater should sink.
- The saltwater is denser than the egg, so it holds up the egg, causing it to float. The freshwater is less dense than the egg, so it can't hold up the egg, and the egg sinks.