Tuesday, September 11, 2012

Ocean Currents

The objective in this lesson is to teach that water in the ocean is on the move and that ONE of the things that causes currents is differences in temperature in one location of the ocean from another.

First explain to young children that wind is a current in the air, so ocean currents are a bit like wind for fish and other sea creatures.  This is different from waves (though currents can have an impact on wave action too).

While there are many things that can all play a part in causing our ocean's currents and the direction they take, one of the main things that causes these currents is temperature differences.


Two tall glass containers such as mason jars or pitchers that can be seen through clearly.
Food coloring
Heat Lamp
A Baking Dish such as a brownie pan or casserole dish

What to Do:

Start by filling your two upright containers about equally full of water.
Place the heat lamp so it will heat the top portion of one of the containers pretty rapidly (mind safety with your child around the lamp)  Near that container so the two can be seen together, but not touching, put ice in the top of the other container.

Have your child ready to watch closely.  Drop an equal number of food coloring drops into both containers quickly.  If you enlist the help of you child or student best at following directions you can drop the drops in at exactly the same time (drop the food coloring in as close to simultaneously as you can make it).

Watch how the food coloring mixes into the water.  Particularly in the cold jar you will see areas where the water is clearly sinking and others where it is clearly being pushed upward.  This is because cold water is denser than warmer water and will sink.  As you can see from the picture (and will see in your demonstration), the water in the jar with ice mixes faster.

Now reverse the experiment.  Pour the ice water into your casserole dish and the warm water onto a house plant and start with fresh clear water in each upright container.  Move the lamp so it is near the bottom of one of the containers and give it a little time to start warming up the water below.  Do not do this over a burner unless you have chemwear (Chemistry glass beakers or flasks) or Pyrex that is safe for heating so you don't wind up with a broken container and a dangerous situation.  If you do have these special supplies, by all means, use a burner.  Place the second pitcher in the ice water (now your temperature differentials are at the bottom of the "ocean".  Run the experiment again, watch for convection (or currents) and compare your outcomes.

Other Things that Cause Currents or impact their direction:

The Tides
Differences in Salinity (Bill Nye the Science Guy Video clip about Thermohaline currents)
The Earth's Rotation and other friction factors
The Shape of the Coastline

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