TPT WebSights column draft for March, 2006:
WebSights features reviews of select sites presenting physics
teaching strategies, as well as shorter announcements of sites of interest to
physics teachers. All sites are
copyright by the authors. This
column is available as a clickable web page at <http://PhysicsEd.BuffaloState.Edu/pubs/WebSights/>.
If you have
successfully used a site to teach physics that you feel is outstanding and
appropriate for WebSights,
please email me the URL and describe how you use it to teach. The best site monthly will receive a
T-shirt. <macisadl@buffalostate.edu>.
Vibrating
Guitar Strings Activity using website data: The
D'Addario guitar string manufacturer company has a considerable set of
technical resources available from their website <http://www.daddario.com/>, including a string tension table at <http://www.daddariostrings.com/Resources/JDCDAD/images/tension_chart.pdf>. J.
Lynch of Wheeling Jesuit University Physics describes how he uses this table
for teaching resonance in strings as part of his introductory physics course:
The manufacturer
has provided a table with the string gauges d (in mils) and the string tensions
FT (in lbs.) for a number of frequencies. The last three digits in
the item numbers indicate string gauge. The plain steel strings are made of
steel alone which our textbook indicates has a density of D=7800kg/m3. Wound strings are avoided because
their linear density cannot be obtained from the available information. My students are given the assignment of
deriving, with some help, the expression for the fundamental frequency f1
of a vibrating guitar
string. On most guitars, the length of the stretched string L is exactly
25½inches.
A brief list of
plain steel guitar strings and string tensions are given to the students who
are assigned to calculate the frequencies. The strings and tensions are chosen
to correspond to standard tuning where the 1st, 2nd, and
3rd strings are tuned to the notes of eÕ (f1=329.63Hz), b (f1=246.94Hz), and g (f1=196.00Hz), respectively. The 4th, 5th,
and 6th strings on a guitar are wound.
The calculated
frequencies always agree very closely with the values in the table because
these values are obtained from the same equation.
Kepler's Third Law Activity using the NASA J-SAT
website to collect data:
Lynch also teaches with the NASA
satellite tracking page at <http://science.nasa.gov/Realtime/JTrack/3D/AppletFrame.html>, which visually tracks about 700 satellites out
of thousands swarming about our earth. Click and drag to change your point of
view. Zoom in by selecting Zoom in from the View submenu. Pick a satellite by either clicking on
the satellite or choosing Select from the Satellite submenu. To watch the satellite move, speed
it up by selecting Timing from the Options submenu. Raise the update rate by selecting Update Rate from the Options
submenu. A little time is needed to gain familiarity with JTrack-3DÕs
features.
Students are given the assignment of calculating the
quantity 
for a list of satellites where T is the orbital period and R is the semimajor axis. It is recommended that the list
cover a range of satellites––from low-orbit to geosynchronous, from
circular to highly eccentric. Include one of the X-ray observatories--XMM or
Chandra–-for curiosity.
The orbital periods are obtained directly by selecting
Satellite Position from the View submenu. The altitudes at perigee and apogee,
hmin and hmax, respectively, can be obtained with some effort by
watching the satellites orbit at a higher time scale. Just before recording
altitude one must slow the satellites down. Once these are obtained then r
R is calculated from R =RE+½(hmin+hmax).where
is the mean radius of the earth.
Students will notice that most satellites orbiting the
Earth fall into one of three types: low-orbit like the space station (TÈ 1½hours),
GPS (TÈ 12hours),
or geosynchronous (TÈ 24hours).
The variety of orbits, notwithstanding, the quantity 
is roughly the
same for most of them: 
.
Both
activities above submitted by John J. Lynch, Physics Dept, Wheeling Jesuit
University, Wheeling WV; <jlynch@wju.edu>
Dan MacIsaac