Let’s start by describing the journey of a pendulum as it moves from one swing to the next. This journey is called a phase. Each phase has three distinct points:
- The positive extreme: when the pendulum is swung up all the way to the right.
- The middle point: where the pendulum is at its lowest point.
- The negative extreme: the pendulum is swung up all the way to the left.
We can also accurately describe the phase as a flow of upward and downward movement—the pendulum swings up, then swings down, back up, and back down, on repeat. Yet, when the pendulum reaches either of the positive or negative extremes (the highest part of the upswings on the right or left side) or the middle point (the lowest point of the swing), there will come a point where the pendulum stops rising and falling.
At these three points exist three infinitesimally small instants of time wherein the pendulum has no swing, a very un-pendulum thing to do.
At the positive or negative extremes, the pendulum will slow to a stop. The stop is instantaneous, as gravity overcomes the pendulum’s upward momentum and it begins to swing back down. In the process, the pendulum must experience a moment where there is neither a rise nor a fall, or, in lay terms, translates to…stopped motion. The pendulum is suspended in perfect balance between up and down. No motion. No momentum.
Think about that. A point of absolute zero. The instant at which change is about to occur.
Cool, right?
A similar-yet-different phenomenon occurs at the middle point of the pendulum swing. As the pendulum crosses from the positive side to the negative side, it crosses the middle, or lowest, point of the swing. At this point, it is neither moving up nor down. It is moving in only one direction: perpendicular to the vertical access, or, looked at another way, straightforward. Again, a very un-pendulum thing to do. If you were to cut the pendulum loose at exactly this point, it would travel away from you in a straight line.
To recap, the phase of a pendulum, which swings in perpetual motion, has one point of zero swing, and two points of zero motion.
So cool.
Right?
Right.