Finger and Branching Patterns in Liquids

This picture shows what happens when air is forced into a ``gooey'' fluid, in this case glycerol. (If you visit our museum exhibit, you can do this experiment in person.)

In the picture there are two pieces of round plastic (23 inches diameter, and 1/2 inch thick) separated by about 1/80 of an inch. Around the circumference of the cell, you can see faintly the positions of the six clamps used to hold the pieces of plastic together.

At the beginning of the experiment, the thin space between the plates is filled with glycerol dyed with food color. Through a tube attached to the center of the top plate air is injected.

As the air enters the space between the plates, it displaces the glycerol and leaves the ``fingering'' pattern shown.

In this experiment, the air was injected, pulled back through the hose, and then injected again. The second injection shows as the whiter fingers; the first injection went further. At the edge of the cell smaller fingers penetrating inwards are visible. They occur because with every injection the two plates separate a little, and air can enter at the sides as well.

In this movie you will see a similar experiment, one that produces fingering patterns as colored water is forced into oil (50 weight motor oil). The spacing between the plates in this experiment is again about 1/80-th of an inch, but the diameter of the cell this time is 12 inches.

The liquid fingering experiment has been used to explore a variety In which other experiment have you seen such branches?

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