- Fill the glass half full with tap water.
- Slowly and carefully place the egg in the water. What happens?
- Add the salt to the water 1 tablespoon (15 ml) at a time. Continue adding salt until the egg floats.
- When the egg floats, slowly fill the glass almost full with water by dribbling spoonfuls of tap water down the side of the glass. This must be done slowly so the waters do not mix. What happens to the egg when the glass is almost full?
When you put the egg in the glass of tap water, it sank to the bottom because an egg is denser than freshwater. When you added salt to the water, the egg floated because an egg is less dense than salt water. When you slowly added more tap water to the glass, the egg appeared to float in the middle of the glass. It was actually floating on the salt water, which had a layer of tap water above it. In the same way, it is easier for a person to float in the ocean’s salt water than in the water in a swimming pool.(From the book: “Science in Seconds at the Beach” by Jean Potter)