If you’re lucky enough to take a swim at the seashore or in the Great Salt Lake in Utah, you can do this experiment first and then you can answer this question:
“Why is it Easier to Float in the Ocean Than in a Swimming Pool?”*
2 clear plastic bowls
blue food coloring
10 tablespoons salt
- Fill both plastic bowls half way with tap water.
- Add a few drops of food coloring to the water in one bowl.
- Mix the salt into the colored water. (this is your “ocean” bowl).
- Stir until the salt is all or mostly dissolved.
- Place an egg in each bowl of water.
What happens to the eggs?
Ideally, the egg in the salt water had buoyancy, (or floated) but the egg in the fresh water sank to the bottom. If the egg in the salt water did not float, keep adding salt to the water until it does.
Salt water is denser than fresh water. (the molecules in the salt-water solution are packed closer together) The egg floated, or had buoyancy because the density of the egg was less than the density of the salt water. It is easier for your body to float or become buoyant in the ocean than in fresh water for the same reason. The ocean is full of salt, so it is denser than fresh water.
Basic Science Vocabulary:
Dense: having tiny parts (molecules) that are very close together.
Solution: two or more substances that are close together. The salt and water mixed together make a solution.
Buoyancy: ability of an object to stay afloat.
*from Nature in a Nutshell for Kids, by Jean Potter.