If you want to help your students understand why you float in the Great Salt Lake, you can demonstrate how an egg floats in fresh water and salt water. In fresh water the egg will sink because because the egg is more dense than fresh water. As you add salt to the water you are increasing the density of the water (you need to add a lot of salt).  When the water density becomes greater then the egg's density the egg will float. Density is a measure of how much stuff you can fit into a defined space.

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Thanks to Mrs. Pierce (4th grade) for the egg-cellent suggestion!