Friday, July 26, 2019

Episode 483 (7-29-19): Buoyancy and Drag are in Play during the Work of Water Exercise

Click to listen to episode (5:11)

Sections below are the following:
Transcript of Audio
Audio Notes and Acknowledgments
Related Water Radio Episodes
For Virginia Teachers (Relevant SOLs, etc.).

Unless otherwise noted, all Web addresses mentioned were functional as of 7-26-19.


From the Cumberland Gap to the Atlantic Ocean, this is Virginia Water Radio for the week of July 29, 2019.

SOUNDS – ~ 6 sec

This week, the sounds of summertime swimming open an episode on water, exercise, and work, written particularly for Virginia students in middle school Physical Science and in high school Physics.

In physics, work is defined as the application of a force to move an object over some distance. Exercise means movement—of oneself or of objects—so exercise results in work in that physics sense.  And the work required, in turn, affects the energy one expends during the exercise.

Have a listen for about 25 seconds to several aquatic exercise activities, and see if you know two physical properties that significantly change the work involved in water exercise compared to exercise on land.  And here’s a hint: if you guess these, you’ll be buoyed up, not dragged down.

SOUNDS - ~ 25 sec

If you guessed buoyancy and drag, you’re right!  You heard diving, swimming, paddling a kayak, and a water exercise class that included walking, running, calisthenics, and moving various objects.  In all of those situations, the effects of buoyancy and drag in fluids—that is, liquids and gases—make water a very different exercise medium from air: in some ways requiring less work, while in other ways requiring more.

Let’s consider buoyancy first.  Buoyant force in water results from the displacement of water by an object in the water.  An object of a given volume will displace that volume of water.  The amount of buoyant force results from the weight of that volume of displaced water.  The effect of the buoyant force depends on another physical property, density—that is, the weight of a given volume of an object or substance.  If the object’s overall density is less than the density of water, the object can float.  Water exerts a greater buoyant force than air, so during shallow water exercise, that greater buoyant force decreases the work one does against gravity.  But in deeper water buoyancy can add the work of keeping oneself upright

Next let’s consider drag, which slows an object moving through a fluid.  Drag results from the viscosity of a fluid, which is the internal friction that affects how a fluid flows.  Water has a higher viscosity than air—just as honey and molasses have higher viscosities than water—so water exerts more drag on a moving object than air does.  The greater drag in water increases the work needed for movements during water exercise compared to the same movements in the air.

As an example, consider a jumping jack in chest-deep water.  Buoyancy reduces the work needed to jump off the bottom of the pool, and it reduces the impact of landing back on the bottom.  On the other hand, drag increases the work done by the arms, legs, and torso moving through the water.

We close by challenging you to think about another example, one that you might well experience this summer.  Try to apply the concepts of buoyancy and drag to a spring-board diver...

SOUND - ~ 3 sec – diving board

...rapidly passing through air and then plunging into water,

SOUND - ~ 2 sec – splash


Virginia Water Radio is produced by the Virginia Water Resources Research Center, part of Virginia Tech’s College of Natural Resources and Environment.  For more Virginia water sounds, music, or information, visit us online at, or call the Water Center at (540) 231-5624.  Thanks to Ben Cosgrove for his version of “Shenandoah” to open and close the show.  In Blacksburg, I’m Alan Raflo, thanking you for listening, and wishing you health, wisdom, and good water.


The opening swimming sounds and the water exercise class sounds were recorded in Blacksburg, Va., on July 24, 2019.

The other swimming sounds were recorded at the Virginia Tech swimming team’s practice in Christiansburg, Va., on April 11, 2014.  The diving board sound was recorded at a Virginia Tech swim meet in Christiansburg on November 21, 2014.  Virginia Water Radio thanks the team and their coaches at that time for their help and for their permission to record and use these sounds.

The kayak paddling sound was recorded on the Potomac River on July 11, 2010.

Click here if you’d like to hear the full version (2 min./22 sec.) of the “Shenandoah” arrangement/performance by Ben Cosgrove that opens and closes this episode.  More information about Mr. Cosgrove is available online at


Diagram of the attraction between the hydrogen and oxygen atoms of water molecules. Water’s molecular structure, along with environmental conditions, determines viscosity and many other properties.  Image from U.S. Geological Survey “Water Science School/Water Properties Photo Gallery, online at Specific URL for this image is


Used for Audio

American Meteorological Society, “Glossary of Meteorology/Buoyancy,” online at

Aquatic Exercise Association, Aquatic Fitness Professional Manual (Seventh Edition), Human Kinetics, Champaign, Ill., 2018; particularly Chapter 6, “Physical Laws as Applied to the Aquatic Environment,” pages 105-125.

Encyclopedia Britannica, “Work,” online at

Indianapolis Public Library “Kids Blog/Density-Buoyancy,” 10/8/13, online at

Lumen Learning, “Fluid Dynamics and Its Biological and Medical Applications/Motion of an Object in a Viscous Fluid,” online at

Merriam-Webster Dictionary, “Viscosity,” online at

Rader’s, “All Work and No Play,” online at

Science Learning Hub (Government of New Zealand), “Viscosity,” online at

Lorena Torres-Ronda and Xavi Schelling i del Alcázar, “The Properties of Water and their Applications for Training,” Journal of Human Kinetics, Vol. 44, 12/9/14, pages 237-248; accessed online at (subscription may be necessary).

For More Information about Physical Properties of Water

Darren Bagley, “Teaching kids about science with water balloons,” Michigan State University Extension, 8/15/14, online at

U.S. Geological Survey, “Water Science School,” online at; and “Water Properties Information by Topic,” online at

Andrew Z. Jones, “ Education/Density of Common Substances,” online at


All Water Radio episodes are listed by category at the Index link above (  See particularly the “Recreation” and “Science” subject categories.

Following are links to other episodes on physical and chemical properties of water.

Episode 195, 1/6/14 – Wading into the New Year, the New River, and Water Thermodynamics.
Episode 210, 4/21/14 – In “Woman Named Whiskey” by The Floorboards, What’s the Solution? (on water as a solvent).
Episode 207, 3/31/14 – Air, Water, and Fire (on relative humidity).
Episode 217, 6/9/14 – Surface Tension and Other Aspects of Water Sticking Together.
Episode 250, 1/26/15 – Reaching the Boiling Point.
Episode 255, 3/2/15 – Density’s in Action in Falling, Floating, and Sinking.
Episode 299, 1/18/16 – Taking an Underwater Dive, Featuring “Scuba Dive” by Kat Mills (discussing buoyancy, density, drag, pressure, and temperature).
Episode 313, 4/25/16 – Evaporating Water Helps Bees Turn Nectar into Honey.
Episode 333, 9/12/16 – Dissolved Gases are Part of the Solution for Creatures Living in Water.
Episode 403, 1/15/18 – At the Freezing Point.
Episode 404, 1/22/18 – Ice on the Pond.
Episode 406, 2/5/18 – Ice on the River.
Episode 407, 2/12/18 – Snow Shows Chemistry and Physics at Work.
Episode 450, 12/10/18 – Neurons, Ions, and Water.

Following is a link to a previous episode on water and exercise.

Episode 466, 4/1/19 – On Water, Biology, and Basketball.


The episode—the audio, extra information, or sources—may help with the following Virginia Standards of Learning (SOLs).

2010 Science SOLs

Grades K-6 Force, Motion, and Energy Theme
4.2 – characteristics and interactions of moving objects (including that moving objects have kinetic energy).

Grades K-6 Matter Theme
K.5 – water properties, including flowing, objects floating or sinking, and water occurring in different phases.
2.3 – properties of solids, liquids, and gases.
6.5 – properties and characteristics of water and its roles in the human and natural environment.
6.6 – properties of air (including pressure, temperature, and humidity) and structure/dynamics of earth’s atmosphere, including weather topics.

Physical Science Course
PS.1 – understanding scientific reasoning, logic, and the nature of science, including current applications to reinforce science concepts.
PS.2 – nature of matter, including elements and compounds, states of matter, physical and chemical properties.
PS.10 – principles of work, force, and motion.

Chemistry Course
CH.5 – phases of matter, kinetic theory, and forces of attraction, including pressure, temperature, and volume principles and laws.

Physics Course
PH.1 – current applications to reinforce science concepts.
PH.5 – interrelationships among mass, distance, force, and time, including work, power, and energy.

Virginia’s SOLs are available from the Virginia Department of Education, online at

Following are links to other Water Radio episodes (various topics) designed especially for certain K-12 grade levels.

Episode 250, 1-26-15 – on boiling, for kindergarten through 3rd grade.
Episode 255, 3-2-15 – on density, for 5th and 6th grade.
Episode 282, 9-21-15 – on living vs. non-living, for kindergarten.
Episode 309, 3-28-16 – on temperature regulation in animals, for kindergarten through 12th grade.
Episode 333, 9-12-16 – on dissolved gases, especially dissolved oxygen in aquatic habitats, for 5th grade.
Episode 403, 1-15-18 – on freezing and ice, for kindergarten through 3rd grade.
Episode 404, 1-22-18 – on ice on ponds and lakes, for 4th through 8th grade.
Episode 406, 2-5-18 – on ice on rivers, for middle school.
Episode 407, 2-12-18 – on snow chemistry and physics, for high school.