As you move off the north pole down to a more southerly point like Washington, for example, the earth not only rotates under the pendulum, but it carries Washington, the building, and the pendulum, in a great circle about its axis. That is, the motion of the earth is now mixed in a complicated way with the motion of the pendulum. As you can prove if you watch the pendulum for a while, the effect of this is to slow down the apparent rotation of the swing. The further south you go, the slower the apparent rotation gets, and at the equator there is no rotation at all. Below the equator the apparent rotation begins again, but in the opposite direction.
Any pendulum consists of a cable or wire or string and a bob.
Like all pendulums this one loses a bit of energy with each swing due to friction from air currents and vibrations in the cable and other factors. Thus, left to itself the pendulum would swing in shorter and shorter arcs until after a few hours it will decrease almost to zero. To keep the Foucault Pendulum going, one must replace the energy lost with each swing. To do this, two iron collars are attached to the cable near the top. There is a doughnut-shaped electromagnet built into the ceiling, and the iron collar swings back and forth inside the hole of the doughnut.