The ocean is made up of layers of water of different densities. Cold water is denser than warm water, water with salt is denser than fresh water. The more closely packed the molecules in a substance, the denser the substance.
|Sometimes you will see little currents in the straw as one type/color of liquid passes another.|
This week I challenged them to apply the information that they have learned to create four distinct layers in straw cylinders using only colored water and salt.
|Please excuse the messiness of our school table.|
I usually clean it off after every activity, but has been one of those crazy weeks for us.
For this experiment you will need:
- 4 Styrofoam cups or insulated containers
- kosher salt
- plastic straws
- medium raw potato
- medicine droppers
- a package of food coloring
Have students write in their journals a key to the colors:
red-hot and salty
blue-cold and salty
yellow-hot and fresh
green-cold and fresh
Have four containers to hold water and label them as above, adding about 15 drops of the appropriate food coloring to each container. Fill the containers with water, two with hot water and two with cold. Add 1/3 cup of kosher salt to both the red and blue water. Stir. Add ice to the blue and green containers.
|source: Ocean Currents, Catherine Halversen, Kevin Beals, Craig Strang, Lawrence Hall of Science|
Looking at a map, discuss where they think the different types of water might be found.
Cold and salty water is found in Antarctica and the Arctic because the water freezes, leaving the remaining liquid water very salty and cold.
Cold and fresh water is found in places where northern cold rivers drain into the ocean, like in Canada and Siberia.
Warm and salty water is found in areas where the water is warm, but due to the evaporation of water and low river inflow, it is very salty, such as the Mediterranean and Red Seas.
Warm and fresh water is found in places where warm rivers drain into the ocean such as the Amazon and Congo Rivers.
As the waters enter the ocean, they form layers which may last a long time and move long distances.
Originally posted: Feb 18, 2011