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STREAMS, DROPS, AND SWOOSHES

This is an outside project, because we will be squirting water all about.

We have several small plastic pill bottles with tight-fitting caps. Not the "child-proof" caps, because we need to take off the caps in order to do our experiment!

We will separate into groups of three students each, and each student will have one bottle. There are three liquids for this project: cooking oil, water, and thick shampoo (or dishwashing detergent). Each group will have one bottle of each liquid; so line up, and fill your bottles, almost to the top. Put the caps on before going back to your places, so we won't have a bunch of spills. Oil or soap on the floor can be slippery.

Since the bottles aren't filled to the very brim, there will be a little air in them at the top.

Here's the fun part. Invert the bottles. That means to turn them upside down. There will be a bubble by the cap of the bottle, and that bubble will have to rise to the top (which is really the bottom). We want to keep track of the amount of time it takes the bubbles to rise.

It probably rises very fast in the water. We need to know whether the oil bubble or the shampoo bubble is the faster to rise.

Why is it that the oil bubble and the shampoo bubble are slower to rise than the water bubble?

Do you think it could be because the oil and the shampoo are thicker than the water? Do you suppose there is a fancy word for the thickness of some liquids?

Viscosity (pronounced "viss-CAW-city"). Now that is a fancy word. Mr. Webster tells us that the thicker the liquid is, the more viscous it is. (This form of the word is pronounced "VISS-cuss.")

Have you ever heard your parents say anything about "30- weight oil," or "40-weight oil," when they are talking about changing the oil in the car? Have you ever heard them talk about "machine oil," or "sewing-machine oil?"

Machine oil and sewing-machine oil are very thin oils. They are not very viscous. 30-weight oil is quite viscous, because it is "thicker" than machine oil, and 40-weight oil
is even more viscous. Usually, in cars, it is important to put more viscous oil in it in summer time, and the less viscous oil in it in the winter time.

There is a very VERY viscous oil, called "wheel-bearing grease," which is so thick you could cut it with a knife. It is very nasty black stuff. If your car doesn't have it
inside the things that hold the wheels on, it could get too hot and dry in there and ruin the bearings. Then the wheels wouldn't turn smoothly, and after awhile, they would not turn at all.

Oil is very important stuff. Viscosities of oil are very important because different "weights" of oil do different things.

Other liquids have viscosity, also, remember, and at another time, we can do the bubble trick with more different liquids.

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