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What Happens to Oil on the Ocean's Surface?

Try this simple exercise for elementary school students to demonstrate what happens when oil spills and becomes mixed with the ocean.

  • glass jar with tight-fitting lid
  • water
  • half a cup of vegetable oil

1. Fill the jar half full of water, and then add half a cup of vegetable oil. Screw the lid on (tight!). Pass the jar around.

Note that no matter how you handle the jar, up or down, the oil always floats on top of the water (we say that the oil is less dense than the water).

2. Next, start shaking the jar (be careful not to drop it).

The oil and the water appear to be mixing together. This is what happens in the ocean when oil and sea water get mixed up by the waves during strong waves or during a storm.

As you shake the jar, if you watch carefully, you'll see that the oil blobs get smaller and smaller (just as they would on the ocean during a storm that lasted for a long time). At the same time, tiny amounts of water fill up the spaces between the oil blobs. This mixture of oil and water is called emulsified oil or mousse. There is an animal called a moose. There is mousse you put in your hair to style it a certain way. But this mousse is emulsified oil. It is just oil mixed vigorously with water.

3. Set the jar aside and then wait a few minutes. Then take another look at the jar.

As soon as you stop shaking the jar, the oil that was all mixed up with the water will begin to separate out. The oil will once again float up to the top, and the more dense water will stay at the bottom. Oil floats!

The mousse that you make by shaking oil in a jar doesn't last very long. In just several minutes, you'll see that the oil and water split back into separate layers. Usually, once oil that has spilled on the ocean has formed a mousse, it also eventually separates from the water in this way (though it usually takes longer). But sometimes, it stays a mousse. We aren't quite sure why mousse sometimes lasts for a long time and sometimes doesn't. Maybe someday you'll be the one to research this mystery and find the answer!

Cleaning Up

The materials for this experiment are all non-toxic and can be poured down the drain once you've finished the experiment.


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Last updated Tuesday, February 5, 2019 3:51pm PST