The reality of the experiment is that it does not reach that path after twenty-four hours. Why?
Oscillation PathReality is not a perfect laboratory. There are variables in which affect experiments. Foucault noted that the closer one travels to the equator, the more the oscillation follows an oval path. Anything but a perfectly circular path would not have the pendulum traveling in the same path as it was twenty-four hours earlier.GravityFoucault and others work hard to limit variables. They have wire made for them which is strong . . . very strong. This wire is not what you will find in the local hardware store. Even so, this wire will expand over time due to being stretched by the weight of the bob. It may not stretch much, but even slightly, would keep the path from being exactly the same after twenty-four hours.The wire will also expand and contract based on the temperature. True, within a building, that would not be as great as a bridge which is outside. What we learn here is that even the slightest change will keep the pendulum from ending up where it started after twenty-four hours. FrictionInstrument makers attempt to create their parts for such experiments in a manner that will eliminate friction. Unfortunately, in the real world that is impossible. Foucault's pendulum is attaached to a ball that rotates in a socket. It is constructed in such a way as to permit the pendulum to freely move as the socket rotates with the building throughout the day. However, despite all of the grease and any other mechanical tricks, that ball and socket creates friction. That friction will cause the pendulum to slow. It will also cause the pendulum tension will will affect the path it takes. Remember, the path needs to be perfect in order to attain the exact starting path after twenty-four hours.Additionally, the pendulum swings through the air. As it does so, the air emits a force upon the bob and wire. This constant friction also causes the pendulum to sway from its perfect path. After twenty-four hours, the pendulum does not appear to be travling in the same path it once was. Re-Starting the PendulumIn fact, most Foucault pendula do not swing constantly. They need to be re-started often as all of the above cause the pendulum to be inaccurate. A Foucault pendulum, although capable of telling time, is a very imprecise time piece. Foucault developed his experiments not as a time telling function, but rather as a means to demonstrate the spinning of the earth about its axies.
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Last Modified: Monday, 28-Feb-2000 10:26:40 EST |