Theme 4: Please Pass the Salt



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Density is defined as the amount of mass that takes up a certain amount of volume. Adding salt or sugar to water increases its density since there are more particles (mass) packed into a similar amount of space (volume). Cooling water can also increase its density since the particles move more slowly at lower temperatures and will be more packed together. When two substances with different densities are combined, the one with a lower density will float whereas the one with a higher density will sink. The greater the difference in density, the more distinct the layers and the harder it will be to get the two to mix.

Lakes can stratify and form thermal layers during the summer since the sun will heat the water at the surface of the lake more. Since warm water is less dense, it remains at the surface. As the weather gets cooler and the water at the surface cools down, the lake will turn over when the previously stratified layers mix. This process is important as it distributes dissolved oxygen and nutrients throughout the lake, making it possible for organisms at deeper depths to survive.

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Curriculum and Instruction | Engineering | Science and Mathematics Education

Activity 2: A Little Bit Salty



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