Foucault pendulum sharing the rotation of the earth about its own axis, the suspension point of the pendulum traces out a circular path during one sidereal day. At the latitude of Paris, 48 degrees 51 minutes north, a full precession cycle takes just under 32 hours, so after one sidereal day, when the Earth is back in the same orientation as one sidereal day before, the oscillation plane has turned by just over 270 degrees. If the plane of swing was north-south at the outset, it is east-west one sidereal day later. This also implies that there has been exchange of momentum;
Foucault pendulum vector diagrams the article discussing the Coriolis Effect for further details. The motion of ballistics with changing latitude is not helpful to understanding the change with latitude of the observed rotation time of the pendulum. (This discussion point is different from what is stated in the reference book.) There is only one point of connection to the Earth for the swinging pendulum and that point of connection doesn't move in relation to the Earth. Because the plane of the pendulum swing is free to swing in relation to the rotation of the structure of the connection point, the rotation of the Earth