Gregory L Baker,

"All pendulums exhibit such rotation, but for most pendulums this behavior is masked by other more prominent effects. For an ideal Foucault pendulum, the plane of oscillation would be seen as fixed by an observer positioned in the stars. (In this discussion we ignore the rotation of the earth around the sun, and the rotation of the sun around the center of the galaxy, and so forth.) Therefore the earthbound observer sees a slow rotation of the plane of oscillation and it is this remarkable feature of the Foucault pendulum which demonstrates, on a large scale, the rotation of the earth." (Gregory L Baker & Jammes A Blackburn, "The Pendulum: A Case Study in Physics", 2005)

"For very long pendulums the spurious effects are small, and the main concern is the dissipation of energy as the pendulum gradually losses amplitude. However, for short pendulums the spurious effects are, not negligible. After the following literary divertissement, we note some ways that builders of Foucault pendulums have overcome the complicating effects of these limitations and thereby produced workable pendulums that are much smaller than Foucault’s original giant creation." (Gregory L Baker & Jammes A Blackburn, "The Pendulum: A Case Study in Physics", 2005)

"In theory, any earth-based pendulum is a Foucault pendulum. However, a realistic Foucault pendulum is a one that is specially constructed to highlight the rotation of its plane of oscillation due to the earth’s rotation relative to a frame of reference fixed in the stars. That is, the plane of the pendulum’s oscillation is fixed relative to the stars while the earth rotates underneath it." (Gregory L Baker & Jammes A Blackburn, "The Pendulum: A Case Study in Physics", 2005)

 "Pendulum clocks exemplify important physical concepts. The clock needs to have some method of transferring energy to the pendulum to maintain its oscillation. There also needs to be a method whereby the pendulum regulates the motion of the clock. These two requirements are encompassed in one remarkable mechanism called the escapement. The escapement is a marvelous invention in that it makes the pendulum clock one of the first examples of an automaton with self-regulating feedback." (Gregory L Baker & Jammes A Blackburn, "The Pendulum: A Case Study in Physics", 2005)

"The linearized pendulum is therefore equivalent to the spring in that they both are simple harmonic oscillators each with a single frequency and therefore a single spectral component. Occasionally we will refer to a pendulum’s equivalent oscillator or equivalent spring, and by this terminology we will mean the linearized version of that pendulum." (Gregory L Baker & Jammes A Blackburn, "The Pendulum: A Case Study in Physics", 2005)