Monday, June 9, 2014

Episode 217 (6-9-14): Surface Tension and Other Aspects of Water Sticking Together

Click to listen to episode (2:57)

TRANSCRIPT


From the Cumberland Gap to the Atlantic Ocean, this is Virginia Water Radio for the week of June 9, 2014.

This week, we feature more mystery sounds.  Have a listen for about 20 seconds, and see if you can guess what place all these sounds have in common, and what important chemical and physical properties of water we can observe in that place.  And here’s a hint: tiny water striders and towering woody plants both have a stake in the answer.

SOUND

If you guessed that the place was the surface of water, you’re right!  Those were sounds of swimmers, a kayaker’s paddle, feet splashing, and a beaver’s tail slap.  All were breaking the surface of water, but what’s actually there to get broken?  Chemical attractions between hydrogen and oxygen atoms in water molecules create a surface film, also called surface tension, on still or slow-moving water.  Among common liquids, water is second only to mercury in the strength of its surface tension.  Surface tension offers a habitat for the familiar insect called a water strider—whose legs are adapted to push into, but not break, the surface film—and for various other insects, plants, and microbes.  But the molecular attractions among water molecules—or water cohesion—that create surface tension are also at work in other biologically vital places, perhaps most notably in woody plants.  Cohesion, tension, and the closely-related property of adhesion—or attractions between water and other kinds of molecules—together give water the capacity to be moved upward through pores and spaces in plants, including dozens or even hundreds of feet high from the roots to the leaves of tall trees.  For these and other reasons, it’s no exaggeration to say that life as we know it depends on how water sticks together.

For other water sounds and music, and for more Virginia water information, visit our Web site at virginiawaterradio.org, or call us at (540) 231-5463.  From the Virginia Water Resources Research Center in Blacksburg, I’m Alan Raflo, thanking you for listening, and wishing you health, wisdom, and good water.

SHOW NOTES

[All Internet addresses mentioned were functional as of 6/9/14]


A water strider (insect family Gerridae) on a stream in Leesburg, Va., June 25, 2010.  The oval shadows on the stream bottom result from the insect’s legs pushing into the water’s surface film.

Whirligig beetles (insect family Gyrinidae) on the surface of the Big Otter River in Bedford County, Va., June 15, 2013.


The two photos immediately above show a simple kitchen demonstration of surface tension.  In the top photo, cornstarch rests upon the surface film of tap water.  In the bottom photo, the cornstarch has been pulled to the sides of the pan, after a soapy finger touched to the water disrupted the surface tension in the middle of the pan.


Acknowledgments

The swimming sounds were recorded at the Virginia Tech swimming team’s practice on April 11, 2014.  Virginia Water Radio thanks the team and their coaches for their help and for their permission to record and use these sounds.

Sources for this episode

Aquatic Chemistry: An Introduction Emphasizing Chemical Equilibria in Natural Waters
, 2nd Edition, by Werner Stumm and James J. Morgan (New York: John Wiley & Sons, 1981); particularly pp. 603—604.

General Chemistry
, by Linus Pauling (New York: Dover Publications, 1970); particularly chapter 12, “Water.”

Guide to Common Freshwater Invertebrates of North America
, by J. Reese Voshell, Jr. (Blacksburg, Va.: McDonald and Woodward, 2002); particularly pp. 340—341 and 368—369.

Limnology, 2nd Edition
, by Robert G. Wetzel (Philadelphia: Saunders College Publishing, 1983); particularly pp. 13—14 and 139.

“Water Properties and Measurements,”
on the U.S. Geological Survey’s “Water Science School” Web site, at http://water.usgs.gov/edu/waterproperties.html.

Other sources of information about water chemistry and physics

“General Chemistry Help,” Purdue University Department of Chemistry/Bodner Research Web, online at http://chemed.chem.purdue.edu/genchem/topicreview/index.php.

Two previous Virginia Water Radio episodes on the special physical and chemical properties of water:

Episode 210 (4-21-14)
, on water as a solvent.
Episode 199 (2-3-14)
, on water's heat-capacity properties.



Virginia Water News and Other Information
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