This project is a mind-blower! We have several little bottles, all the same size, with tight-fitting caps. The open ends of the bottles are narrower than the bodies, so
that the caps don't stick out farther than the bodies of the bodies. You may have guessed, that we need to be able to roll them, without the bottles getting confused and rolling around in circles.

They are all half-full of liquids; each of the liquids is different in viscosity.

We have a sheet of plywood on the floor, propped up along one side, so that one edge of the board is about 2 inches higher than the other edge.

Several students can take one bottle each, and kneel down at the higher edge of the board. Place the bottles, on their sides, at the edge of the board, so that they can roll down to the floor. At the same time, let the bottles go, and watch what happens.

Are you surprised to see that they all don't roll together? How could this be? They are all the same size, and they are all only half-full. Why don't they roll together?

Let's do it again. To make sure than none of the bottles is pushed; that is, that they all start their roll with the same amount of force, we will have two students hold this yard-stick across the board, at about one inch below the edge. The bottles can rest against the yardstick.

We can say, "One, two, three, GO!" When we say "GO," the students lift the yardstick so that the bottles can roll without being pushed.

Now, do they still roll at different speeds? Which ones are the fast-rollers, and which ones are the slow-rollers?

Looks like water rolls fast, molasses rolls very slowly, nasty wheel-bearing grease rolls slowly and unevenly, because it doesn't even swish around in the bottle. Cooking oil
rolls right along, but not as fast as the water. Corn syrup is another slow one, but it is not as slow as molasses. (There is a saying about that, "...as slow as molasses in
January." Cold temperatures increase viscosity; warm temperatures decrease viscosity.)

We can time the bottle-rolling, and make a graph to illustrate the differences viscosity makes. It's probably best to run this test more than once, and take an average of
the rolling times.

We can even put the bottles in the refrigerator for a little while to cool them, and see if that makes any difference.