Stirring Sand

I ran across the idea for this week's experiment (which is really more of a challenge), while researching another question. The more I thought about it, the more I liked it. It involves the unusual behavior of sand in a glass of water.

To try this, you will need:

- a clear, drinking glass
- water
- sand
- a spoon

Fill the glass about 2/3 with water. Then add couple of pinches of sand. You don't want a lot. About 1/8 of a teaspoon would be about right. In just a minute, we are going to give the glass a good stir. When you stir the water with the spoon, what will happen to the sand? Think about it before you actually try it. Try to predict what will happen. Even better, try to predict WHY it will happen.

Once you have made your prediction, give the glass a good stir. After a few seconds of stirring, remove the spoon, and let the glass sit until the water stops moving. Watch carefully to see what the sand does.

When the water stops moving, you should find that the sand is gathered in the center of the bottom of the glass. Wait a minute! That should not happen! The sand is denser than the water, which is why it sinks instead of floating. When you stir the water, making it spin round and round in the glass, shouldn't the sand be forced to the outside edge? Why would it pile up in the center?

Think about this carefully, and make sure you have a good answer before you go on to part 2.

Have a wonder-filled week.

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