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"Let us strive to make each moment beautiful."
Saint Francis DeSales
painting by Katie Bergenholtz

Ocean Currents, Part V: Ice Cubes Demonstration

The two jars react very differently when the colored ice cubes are added to them.
We have learned in the past few weeks that salt water is more dense than fresh water and that cold water is more dense than warm. How do these factors, salinity and temperature, combine?
Before hand, make some colored ice cubes by adding food coloring to the water in an ice cube tray. We did this the night before.
Fill two identical jars about 3/4 full with tap water. Add about 1/4 cup Kosher salt to one of the jars, mix thoroughly and let sit. Can your students tell which one of them has salt water and one fresh water (without tasting)? Very carefully add 3-4 of the colored ice cubes to each jar. Add the same amount to each jar. Do not bump or disturb the jars.

Where is the colored water going? Which jar is the ice melting faster? What would this indicate?

Can you see a current flowing toward the bottom as the icy water carries the food coloring down with it as it sinks? As the temperature evens out, the food coloring mixes throughout the jar. This is the fresh water jar. The icy water is denser than the room temperature water and sinks. The sinking of the icy water helped set up currents in the jar which quickly mixed the icy water and the room temperature water.

In the other jar the ice melted more slowly and the food coloring formed a layer at the surface. Because the ice cubes were made of fresh water, as they melted, the water floated at the top of the denser salt water.

To demonstrate for the little boys how the salt-water could be more dense than fresh water, I took a cup with some marbles in it and told them that this is just like the water molecules and then added some salt to the cup. This is like the salt molecules, which are able to fit in between the water molecules, making the entire substance more dense.
The densest water in the ocean is formed around the Antarctica because the water is very cold and very salty. This combination causes it to become very dense and sink to the bottom of the ocean basin surrounding Antarctica. This water then travels north as the densest water in the ocean.


Ocean Currents, Part VI: Layering Liquids
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6 comments:

  1. That's cool. I'll have to try this soon.

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  2. Next year, we are going to work on Marco Polo and I am defintely adding your terrific water study.

    Thanks a million!
    Bethany

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  3. Oh...I forgot to ask. Do you have a book list of children's lit that you are using to study oceans?

    Bethany

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  4. These ocean experiments have been just excellent!

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  5. A great experiment for an ocean study.

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  6. Way too cool. I've had this sitting open on my browser since Friday, and this is my first time to read anybody's posts.

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