So over the time of a 24-hour day, the Foucault Pendulum will appear to gradually sweep out a 360 degree circle. Some reputable physicists say that we really don't know. So a body that is still will not move, unless a force tries to push it. In another example of Newton's First Law, a body that is moving will keep on moving, unless an external force tries to stop it. This desire of a body to keep on doing whatever it's doing, is called inertia .
Nobody really understands what inertia is.
The traditional explanations involve some circular reasoning. The reasoning goes like this. A body will keep on doing whatever it's doing is because of its inertia. And inertia is the tendency of a body to keep on doing whatever it's doing. Because of its inertia.