Capillary Action
http://ga.water.usgs.gov/edu/capillaryaction.html
Even if you've never heard of capillary action, it is still
important in your life. Capillary action is important for moving water (and all
of the things that are dissolved in it) around. It is defined as the movement
of water within the spaces of a porous material due to the forces of adhesion,
cohesion, and surface tension.Capillary action occurs because water is sticky, thanks to
the forces of cohesion (water molecules like to stay close together) and
adhesion (water molecules are attracted and stick to other substances).
Adhesion of water to the walls of a vessel will cause an upward force on the
liquid at the edges and result in a meniscus which turns upward. The height to which capillary action will take water in a uniform
circular tube (picture to left) is limited by surface tension and, of course,
gravity.
When you spill your glass of drink on the kitchen table you
rush to get a paper towel to wipe it up. First, you can thank surface tension,
which keeps the liquid in a nice puddle on the table, instead of a thin film of
sugary goo that spreads out onto the floor. When you put the paper towel onto
your mess the liquid adheres itself to the paper fibers and the liquid moves to
the spaces between and inside of the fibers - thank capillary action!
Plants and trees couldn't thrive without capillary action.
Plants put down roots into the soil which are capable of carrying water from
the soil up into the plant. Water, which contains dissolved nutrients, gets
inside the roots and starts climbing up the plant tissue.
The proof is
in the .... celery
In the experiment, the students will get to see water climb up narrow glass capillary tubes and also climb through the capillary tubes in celery stalks. The students will also observe the celery stalks or white carnations change color over time. Therefore, the students will be learning about making observations and logging their results as they observe the stalks and flowers over the week.
You can see capillary action in action (although slowly) by doing
an experiment where you place the bottom of a celery stalk in a glass of water
with food coloring and watch for the movement of the color to the top leaves of
the celery. You might want to use a piece of celery that has begun to whither,
as it is in need of a quick drink. It can take a few days, but, as these
pictures show, the colored water is "drawn" upward, against the pull
of gravity. This effect happens because, in plants, water molecules move through
narrow tubes that are called capillaries (or xylem).
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