Pendulum is a very simple device:
You have a weight hanging from a thread that is attached to a point that can swing freely in every direction.
To make the pendulum move, you pull the weight sideways and let it go. It starts swinging back and forth and keeps on doing it until the friction caused by air resistance against the weight, together with the friction caused by the connection between the thread and its attachment point, eventually slows it down all the way to a complete stop.
By making the thread very long and the weight very heavy the effect of these tiny frictional forces can be minimized, and it is fairly simple to create large enough pendulum that keeps on rocking for days.
The pendulum per se is a simple demonstration of two kinds of energy:
Any object that is being moved upwards against the gravity of the Earth gains potential energy, which can be recovered if the altitude is reduced again.
When an object with potential energy is let go in a gravity field, the pull of gravity accelerates it as if falls, turning the potential energy into kinetic energy.
Therefore when the pendulum is pulled to the side, we are adding potential energy to it as we move the weight higher against the gravity of the Earth. And when we let it go, gravity takes over and starts pulling it towards its lowest position again. During this downward swing, the potential energy of the pendulum is converted into kinetic energy. In short, the pendulum gains speed, which causes it to swing past its “rest position” and continue upwards again, this time converting the kinetic energy back to potential energy.
Eventually it reaches its highest extension on the other side of the swing, which is always at least a tiny bit lower than its previous height due to all the frictional forces, and then the same process repeats itself in reverse.
The reason why it keeps on rocking can be derived from Newton's First Law, which states:
“An object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.”
In the case of a pendulum, the motion eventually stops due to friction, and the speed of the movement is constantly affected due to gravity as potential energy is turned into kinetic energy and vice versa, but unless the air around it is very turbulent, the direction of the swings remains the same as per the law above: nothing is trying to turn a pendulum sideways,so its momentum keeps its direction stable.
Yet, every Foucault's Pendulum in the world eventually appears to turn also sideways as time goes by.
Except if one is installed on the equator.
There is also one distinct difference in the behavior of Foucault's Pendulum between the hemispheres: the ones on the northern hemisphere appear to drift clockwise, whereas the ones in the southern hemisphere drift in a counterclockwise direction.
Every Foucault's Pendulum also moves slightly differently over time, and this difference can be observed to depend on the latitude of the installation.
As the Newton's First Law has been proven to be correct gazillion times, there has to be some other reason for this change of orientation, and the fact that there is no sideways motion on the equator should give enough hint on what might be behind this behavior.
If you look at this from the Flat Earth Model point of view, Foucault's Pendulum presents a problem that simply can't be explained away:
The pendulum is hanging freely. Check.
It is attached to a stationary building. Check.
It is heavy enough so that any changes in air circulation around it will not cause a change of direction. Check.
The building sits on top of a flat, stationary Earth that does not move. Check.
In the Globe Earth Model, there is just one change to the observations above:
The building does not sit on top of a flat, stationary Earth that does not move, instead, the building containing the pendulum is attached to a rotating Earth.
So the explanation for this weird behavior is actually very simple: the pendulum faithfully follows the Newton's First Law, keeping the direction of its swing, but as its movement is not constrained in any way by its attachment point, the Earth is slowly rotating below it while it swings. Anybody observing the pendulum is also rotating, so they can't feel any change in their own point of view, thus it appears that the pendulum itself is changing direction.
Yet it is you, the building and the planet below the building moves, not the pendulum.
Next time you visit a science museum that has this kind of demonstrator, take a look at the direction of the pendulum when you enter the exhibitions, and take another look right after you leave. You have witnessed a proof of the fact that the Earth below your feed is not stationary.
There are hundreds of Foucaul't Pendulums in the world, so finding one is not hard:
This behavior, on its own, does not yet prove that we live on a giant ball, but by comparing the movements of different Foucault's Pendulums at different latitudes on Earth you can create a mathematical model for the movement that can only be explained out by a spherical Earth.
And if the pendulum resides on the equator, there is no sideways force turning it: the equator is in exact 90 degree angle against the rotational axis of the Earth.
We can safely say that every Foucault's Pendulum in the world proves at least that the claim of a completely motionless, flat Earth below our feet is false: whatever we are standing on appears to move, because a pendulum swinging over a stationary Earth should not show any sideways movement.
The reason behind this, as per the Globe Earth Model, is the Coriolis force, caused by the rotation of the Earth. The same force that snipers have to take into account, as mentioned in the book. Coriolis force also causes the hurricanes on Earth rotate clockwise on the northern hemisphere and counterclockwise on the southern hemisphere, matching the observed direction of the drift of the pendulums.
As for the Flat Earth Model, neither the drift of the pendulums nor the rotational direction of hurricanes can be explained out, as there should be no difference of any kind between the hemispheres if the ground below is stationary.
Foucault's Pendulum in Barcelona knocks down sticks as the Earth turns below it.