It can be hard to understand why salt water lets objects easily float on its surface. This salt water density science experiment will let your kids observe the water in action.
Two clear containers
Two eggs or pair of matching items
Fill two containers with equal amounts of tap water. In one container, add 6 tablespoons of salt, and mix well until it dissolves. Place one egg (or other item of your choosing) in the two containers.
What do you see? Which water makes the item float, and which one sink?
Things to discuss (from Little Bins, Little Hands)
WHAT IS DENSITY?
So explaining salt water density to a preschooler is not the easiest task, but you can show that two things of similar size can weigh different amounts and that is what causes things to sink or float. Things that have a higher density may sink and things with a lower density may float.
WHAT DOES SALT DO TO THE WATER?
Ok, so obviously we know that salt makes the water more dense allowing more types of objects float when they might not in fresh water. Fresh water is less dense so many things sink.
WHY DOES THE SALT INCREASE THE DENSITY?
As the salt dissolves in the water, it adds mass (more weight to the water)! This makes the water more dense and thus allows more objects to float on the surface.
To further this visualization, you can get some food coloring, and another small container. Add a little tap water and salt and mix to dissolve, and mix in a few drops of food coloring.
Then using a dropper or careful hands, add the colored salt water to the fresh water, and let the water organize itself. You'll see the colored water sink to the bottom of the container, furthering the point that salt water is denser than fresh water.
For more information and details about the science behind density, check out this link.
Resources and References
“Density Facts for Kids.” Wicca for Kids - Kiddle, kids.kiddle.co/Density.
Emma, and A. Creighton. “Salt Water Density Science Experiment for Kids.” Little Bins for Little Hands, 3 Oct. 2016, littlebinsforlittlehands.com/simple-salt-water-density-science-experiment-saturday-science/.