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If you have the advantage of visiting the ocean or the Great Salt Lake in Utah this summer, you may find your swimming experience in these bodies of water to be slightly different than swimming in a freshwater lake or river. If you accidentally get water in your mouth or eyes from the ocean or the Great Salt Lake, you will certainly notice the saltiness of the water. But what about floating? Is it easier to float in the ocean or Great Salt Lake than in freshwater? And if there is a difference in your ability to float, do you think that water from one body of water is denser than water from another body of water? Which do you think is the most dense? Freshwater from a lake, saltwater from the ocean, or saltwater from the Great Salt Lake? Do this experiment to find out!
Density is the measure of how much matter (mass) is packed into an item or material compared to the amount of space (volume) it takes up. A material that is more dense (e.g. lead) will weigh more than a material that is less dense (e.g. cork) even though they both take up the same amount of space. Or, to think of density another way, 10 pounds of cork takes up a lot more space than 10 pounds of lead.
In this experiment, the salt added to the "ocean water" and "Great Salt Lake water" caused these solutions to contain more matter than what was in the freshwater even though the different types of water still took up the same amount of space. The more salt in a solution, the more dense or "heavier" it is, and the less salt in a solution, the the less dense or "lighter" it is. This allows the "ocean water" to float on top of the "Great Salt Lake water" and the freshwater to float on top of the "ocean water."
To really prove that the "Great Salt Lake water" is the most dense, the freshwater is the least dense, and the "ocean water" has a density somewhere in between these two types of water, try this experiment again except this time reverse the order that the solutions were placed in the graduated cylinder. Do they sit on top of each other as they did before or do they mix up?