What You'll Need:
- Fresh (tap) water
- Regular salt
- Three large clear glasses (at least 16 oz)
- 1 raw egg, right out of the fridge, still in the shell
- Food coloring (optional)
What To Do:
- Create a solution of salt water by stirring 2 tablespoons of salt into 8 ounces of water in a glass. Add a few drops of food coloring.
- Gently place the egg in the glass and notice that it floats. (If it sinks, add more salt.)
- Fill another glass a little less than halfway with regular water. Add a few drops of a different color.
- Move the egg from the salt water to the fresh water and watch it sink.
- Put the egg aside and slowly pour the fresh water on top of the salt water. Tilt the glass of salt water as you pour so that the salt water and fresh water don’t mix.
- Slowly drop the egg into the glass and watch as it falls through the layer of fresh water and stops on top of the salt water.
You’re seeing density in action. Density is the amount of matter (the science word for stuff) that you can pack into a certain amount of space. Things that are denser than water sink; things that are less dense float. Adding salt to water makes it denser. The egg hovers between the two layers because the egg is less dense than the salt water but more dense than the fresh water. Have you heard the riddle, “Which weighs more, a pound of feathers or a pound of bricks?” They both weigh the same: a pound! But a pound of feathers would take up more space than a pound of bricks. That’s because bricks are denser than feathers.
Our expert: Caitlin Drechsler, 5th and 6th grade science teacher at Buckingham Browne & Nichols in Cambridge, MA