Physics: Experiment of the
Month
Physics: Experiment of the
Month
Our Science Design driven pendulum has been running for three years now. There is also a traditional monumental Foucault pendulum online, the Kirchhoff Instutute of the University at Heidelberg
The inspiration for this
project was three-fold:
1) The new science building at Millersville has a three story stairwell
which cried out for a Foucault pendulum, but there was no money available for
the standard monumental version (cost between $50,000 and $100,000).
2) Dr.
Nolan found an article by Richard Crane showing that a short driven Foucault
pendulum could be built. The reference is:
A Foucault Pendulum "Wall
Clock"
by Richard H. Crane
American Journal of Physics 63, (1) 33-39
(1995).
3)Meron Wollie
showed
that we can parametrically drive a short pendulum with equipment readily at
hand
The rotation of the plane of oscillation of the Foucault pendulum is the most immediate and convincing evidence that the earth turns on its axis. The figure shows the 1 meter driven Foucault pendulum in operation in the Physics laboratories of Millersville University. The pendulum oscillates with a period of 2 seconds. The figure is updated at a rate of approximately (on the computer clock) once each 101 seconds. To see the latest figure, click on the refresh (or reload) button of your browser. (Some internet services cache the page that you view and refuse to truly refresh. If this happens, open Netscape or Explorer and view the real time image in one of those browsers.)
Click here for a short movie of one of our pendulums as it swings.
To see a live sequence here. Log in as guest, with password guest. Choose the Java button to see the pendulum in motion. As we tweak the set-up, we will bump the pendulum, so it may not be turning properly for a while. This nice development was made by our technician, Shawn Reinfried. We were encouraged to try it by Doug Bowman, a workshop participant who found a way to put multiple images of his pendulum on the web.
Because the period is not an even fraction of the update time period, each image will show the pendulum in a slightly different position. A few refresh cycles will give a sense of how the pendulum is swinging. At Millersville's latitude of about 40 degrees North, the pendulum should take about 36 hours to precess through an entire 360 degrees, meaning that it should precess about 10 degrees per hour.
The rate of rotation of the plane of oscillation is not constant, partly because of imperfections in the pivot point. More interestingly, the driving mechanism pulls up on the pivot each time the pendulum passes its low point. The brief upward velocity couples via the Coriolis force to induce a slight elliptical component to the motion. The elliptical path is clockwise because the direction of the Corioilis force. Because the period of the pendulum is slightly amplitude-dependent, the elliptical path precesses clockwise. Thus, the times marked on the scale below the pendulum must be regarded as an idealization. Our pendulum routinely turns a little bit fast.
The parametric drive mechanism used here is not the most common method of keeping up the motion of the pendulum. A monumental pendulum using a parametric drive was built in 1988 by Sir Brian Pippard, a physicist noted for his work on the properties of electrons in metals. Information on Pippard's pendulum may be found here.
A
traveling version of the pendulum, designed by Steven Nault, is now available
at Millersville for visits to schools in the region. If interested, plan on
keeping the pendulum on display for a period between 1 and 3 months. The
pendulum needs about 1 square meter of floor space, and is about 2 meters high.
It should be placed on a floor which does not vibrate. Contact
john.dooley@millersville.edu for detailed information.
Click here for a 19MB quicktime movie of a 3 meter prototype of a 10 meter pendulum that is being built for the new Lancaster (Pennsylvania) Science Factory museum.
Click here for a bookmark with a quick explanation of the Foucault pendulum.
Click here for teaching suggestions for integrating the driven pendulum into an introductory physics course.
Click here for a discussion of the rotation of the plane of oscillation of the pendulum.
Click here for a discussion of how elliptical motion can make the pendulum plane rotate "too fast."
Click here for a large figure, showing 12 photos of one of our pendulums, in various positions throughout a single day.
Click here for a discussion of the driving mechanism.
Click here for details on making a Foucault pendulum in your basement.
For a minute-by-minute record of another kind of real-time earthly motion, check out the MU Earth Science Seismograph page.
The precession of a pendulum has a certain artistic appeal, as illustrated here http://web.njit.edu/~jcl7/pastimes/pendulum/index.html
Comments:
physics@millersville.edu
Page maintained by: J. W. Dooley
to Physics
Homepage