We all know that plants “drink” water with their roots. But the roots are way down at the bottom, and that water has to be dispersed through the whole tree, all the way up to the tippity-toppest leaves. How does that work? The answer, homeboy or homegirl, is capillary action. This easy lil’ experiment will help you demonstrate to students the mechanics involved in this process.
You Can’t Lose When You Choose to Ooze
For startsies, you’ll need two drinking glasses, some paper towels, water, and a tray on or a sink in which to place the whole shebang to avoid spillage—a tray is better because it’s easier to view from all angles, but work with what you’ve got. Gather your smelly little students ‘round and commence thusly:
Put one of the drinking glasses—we’ll call it Glass A—on a hardcover book or other sturdy platform (add that to your list of supplies, I guess) on/in your tray/sink. Fill Glass A almost completely full with water, then place your second drinking glass—we’ll call this one Glass 2—directly beside Glass A. Stack two loose sheets of paper towel, then twist them up tightly (be careful not to tear them) and, once twisted, bend your creation in half to form a vaguely U-like shape.
From there, place one end of your paper towels in Glass A and the other in Glass 2. Then—and this is the exciting part—just leave it. Maybe keep an eye on it as the water first starts to soak into the paper towels, but after that, yeah, just leave it and go about your other business for a while. At this point I should probably point out that it’s best to begin this experiment early in the day, as it takes a while to get to the payoff.
As the day wears on, the water will, very slowly, just kind of ooze its way through the paper towels and transfer from Glass A to Glass 2. This, in essence, is capillary action.
As you may have noticed, the water moves very slowly in this experiment. This is because it has to travel into and between the hundreds of thousands of spaces between the fibers of the paper towels. Getting into the fibers themselves is no problem for water, but traversing the spaces between those fibers—miniscule though the spaces be—is more difficult and time-consuming.
Similarly, the water a tree “drinks” must move between the millions (probably more like billions or trillions) of fibers that make up the tree. This capillary action is further slowed by the battle against gravity. Water’s powerful surface tension is what makes its movement between fibers possible.