Let's Revive the Study of Fluids
Physics has a long and illustrious history. It could have a brilliant
future, but in the past several years, university physics departments
have experienced problems. Students report that upper−division physics
courses are unnecessarily difficult, and they question the social
relevance of physics. Physics attracts a lower percentage of women and
ethnic minorities than most other fields. Undergraduate enrollments of
physics majors are declining in most US universities.
In some ways, physics is a victim of its own successes. Past
research by physicists allows today's physicists to push tantalizingly
close to the ultimate boundaries of understanding. As a result, many
academic physicists may find research much more interesting than
teaching. The progress and promise of physics also can lead to a type
of arrogance that fails to inspire others.
So much is already known in physics that attempting to digest
significant portions of that knowledge can tax the minds of modern−day
students—who have virtually the same mental capacities, time, and
energy as the students of centuries past who faced a much smaller body
While physics faculty became increasingly concerned about the
undergraduate physics curriculum, new discoveries accelerated our
awareness of the importance of fluids. Can people with vested interests
in fluids and people with vested interests in physics departments gain
anything from each other? To answer this question, I will first explore
The subjects of physical oceanography, dynamic meteorology, and
solid−earth geophysics are all applications of physics. All three
subjects depend on fluid dynamics, and both physical oceanography and
dynamic meteorology are almost totally dependent on fluid dynamics. I
use physical oceanography as an illustrative tool, although dynamic
meteorology or solid−earth geophysics could serve the same purpose.
What is physical oceanography?
At one time, physical oceanography was a descriptive enterprise.
Today, it is a form of classical physics dedicated to increasing our
understanding of physical processes in the oceans. Its practitioners
are classical physicists who affiliate with the culture of
oceanography. This culture exists because of needs for:
- Specialized vessels, docking facilities, buoys, instruments, and associated equipment
- Consideration of the oceans as unified systems in which the
four branches of oceanography (physical, chemical, geological, and
biological) are interdependent
- Convenient channels of communication for scientists who work in any or all of the four branches of oceanography.
Physical oceanography research focuses on scales of motion ranging from
millimeters (the diameters of the smallest turbulent eddies) to
thousands of kilometers (the horizontal dimensions of the ocean
The following phenomena force physical oceanographers to make
air−sea interactions and other boundary conditions integral facets of
- A continuous exchange of gases takes place at the air−sea interface
Winds drive surface waves and currents
- Evaporation and precipitation determine the salinity of sea
water, which acts in concert with variations in temperature
distributions to drive density circulations
- Bottom topograpy directs, accelerates, and decelerates near−bottom currents
- Shear gradients generate turbulence near land boundaries and at boundaries between adjacent water masses
- Near−bottom currents moving over soft bottoms cause sea water to migrate between sediment grains.
Physical oceanography specialties include air−sea interaction,
upper−ocean processes, cascading and bottom water formation, general
circulation, paleocirculation, waves, tides, tsunamis, seiches,
currents, meanders, eddies and rings, shear, turbulence and mixing,
water−column microstructure, nearshore processes, optics, and
Some physicists in ocean optics or acoustics consider themselves as
physical oceanographers, others as traditional physicists. Still others
affiliate with subcultures and consider themselves as optical
oceanographers, acoustical oceanographers, underwater sound physicists,
or underwater sound engineers.
The importance of physical oceanography derives partly from the
importance of the oceans. Photosynthesis in the oceans generates most
of the oxygen we breathe and most of Earth's living biomass. Sea−floor
sediments contain the world's least−disturbed records of the fallout
from past events in the oceans, in the atmosphere, and on land.
Evaporation from the oceans provides most of the precipitation that
allows life to exist on land.
However, physical oceanography also has an impact beyond its role in
ocean physics because biological, chemical, and geological processes in
the oceans depend more heavily on physical processes than physical
processes depend on them.
Patchiness—that is, unevenness in the geographical extent to which
organisms can exist—depends primarily on physical processes that
recycle nutrients and bring them into the sunlit surface waters where
photosynthesis can take place. Seawater chemistry depends on biological
productivity, which depends on physical processes. Geological processes
such as the erosion, transport, and deposition of sediments depend on
physical processes driven by waves, ocean currents, and turbulence.
Undergraduate physics majors at universities study classical
physics topics (such as thermodynamics, mechanics, and optics) that are
required if they choose to enter graduate programs in physical
oceanography. University physics departments are the most important
source of incoming graduate students in physical oceanography.
Most incoming graduate students in physical oceanography have
limited, deficient, or nonexistent backgrounds in fluid dynamics, so
they need to do undergraduate remedial work.
To make optimal contributions to physical oceanography, physics
departments should offer a fluid dynamics option for undergraduate
majors, including an introductory fluid dynamics course requiring as
prerequisites upper−division status and mathematics through
differential equations, and an advanced fluid dynamics course requiring
as prerequisites the introductory course and advanced mathematics for
physicists. Both fluid dynamics courses should offer appropriate
research experience. Physics departments could also raise awareness of
graduate school and career paths in physical oceanography.
Physical oceanography offers a wealth of examples and motivational
opportunities that could be used by professors in teaching
undergraduate physics courses. Students are likely to find the vortices
generated by the conning tower of a moving submarine, the creation and
destruction of beaches, and the physics of surfing to be interesting
and relevant to contemporary life.
Traditional physics provides important conceptual underpinnings for
all branches of science, engineering, and medicine. It provides the
best source of people who enter graduate programs in physical
oceanography, dynamic meteorology, and solid−earth geophysics, each of
which is socially relevant. These direct and indirect contributions
suggest that traditional physics is among the most socially relevant
fields on the planet. Many students do not see physics that way,
however, largely because the seminal character of physics masks its
If physics departments expanded their offerings in fluid dynamics,
they would increase their contributions to social relevance through
their efforts in fluid dynamics itself and by strengthening graduate
programs dependent on fluid dynamics. By doing so, the same departments
would also gain in the visibility of their contributions to society.
Most physics departments have paid little attention to fluids.
Nevertheless, individual scientists have pursued forms of research that
would fit best within the realm of classical physics. For example,
England's Irish−born Osborne Reynolds (1842−1912) and Germany's Ludwig
Prandtl (1875−1953) created flow visualization methods that evolved
into the present−day collection of at least 25 different flow
In doing so, Reynolds and Prandtl facilitated some of the most
important discoveries in modern fluid dynamics. They opened a door
through which physics departments could follow their lead by elevating
fluid dynamics to a standard, universally accepted specialty within
To sample the extent to which present−day university physics
departments have made a commitment in fluid dynamics, I surveyed the
course offerings of 55 US university physics departments using the
virtual library provided by College Source Online. (For course
descriptions, see the website of College Source Online, http://www.cgf.org/home.asp.)
I chose those physics departments that are the largest or best known,
or that are close to oceanographic institutions. Of those departments,
none offered an undergraduate fluid dynamics option. None offered the
two or more upper−division courses that might buttress such an option.
Seven offered one upper−division fluid dynamics course.
Those seven departments have entered the door opened by Reynolds and
Prandtl. They also have opened the same door a bit wider, which
suggests that their actions might represent a wise step forward.
The small percentage of physics departments making a commitment in
fluid dynamics suggests the presence of opportunities. Within these
opportunities, physics departments must find new ways to address the
problems I mentioned earlier. For example, fluid dynamics courses
exhibit modest levels of abstraction and uncertainty, and they possess
the highest possible potentials for exploiting the visualization of
processes. These characteristics should allow physics faculty members
to teach fluid dynamics courses without making them unnecessarily
A ray of sunshine pointed in this direction has been provided by Jerry Gollub (Physics Today, December 2003, page 10),
a professor of physics at Haverford College. He has experimented with
integrating fluid dynamics into physics curricula, has achieved
encouraging results, and offers suggestions that could be used
By expanding into fluid dynamics and benefiting from the experiences
of physicists like Gollub, physics departments could experience the
kind of synergy needed to ensure that stable or increased physics major
enrollments become almost universal.
1. B. J. Korgen, Marine Technology Society Journal 37, 23 (2003).
Ben Korgen was a professor of physical oceanography at the
University of North Carolina and at Tulane University. He then worked
for 20 years as a physical oceanographer in the Naval Oceanographic
Office at the Stennis Space Center in Mississippi before retiring.
Letters and opinions are encouraged and should be sent to Letters,
Physics Today, American Center for Physics, One Physics Ellipse,
College Park, MD 20740−3842 or by e−mail to firstname.lastname@example.org
(using your surname as "Subject"). Please include your affiliation,
mailing address, and daytime phone number. We reserve the right to edit
© 2004 American Institute of Physics