rings in water
Put cold water into a small glass or jar. A 4 ounce jar size
is about right. A larger small mouth jar will also do. Add
5 drops or so of food coloring. A dark color of water soluble
paint can be mixed with the water instead of food coloring.
Or use grape juice. Cover the mouth of the jar with aluminum
foil and fasten it in place with a rubber band or tape. Use a
pencil point to make a hole at the center of the foil. The
hole should be 1/8 inch or so in diameter.
Fill a larger jar with warm water. Turn the small jar over
and place the foil covered mouth just below the surface of the
warm water. Tap on the bottom of the small jar. A ring of
colored water will travel downward through the warm water.
Also try lowering the small jar a tiny amount and immediately
jerking it back. Larger holes require more motion and
produce faster moving rings that quickly hit the jar's bottom.