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How does a pendulum exchange kinetic energy and potential energy as it swings?

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Study how a series of gears in a waterwheel translates a stream's energy to a millstone — energy conversion Before the Industrial Revolution, power came from three main sources: humans, draft animals, and water.
The ingenuity people used in harnessing waterpower can be seen in this medieval-style mill. The waterwheel is turned by a stream and is connected to a shaft that leads into the building. At the other end of the shaft is a gear. The connection of a series of gears translates the power from the stream to a shaft that drives a millstone, which grinds flour from grain.
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A swinging pendulum demonstrates the continuous exchange between kinetic energy (energy of motion) and potential energy (stored energy due to position).12

As the pendulum moves, energy is rhythmically interchanged between these two forms:1

At the vertical position: The pendulum reaches its lowest point and greatest speed. Consequently, it possesses its maximum kinetic energy and minimum potential energy.1
At the extremities of the swing: The pendulum stops briefly at the highest point of its arc. At this moment, its speed is zero, meaning its kinetic energy is zero and all the system's energy is stored as potential energy.12

In an idealized system—one lacking friction or air resistance—the sum of these two energies, known as mechanical energy, remains constant. In real-world applications, dissipative forces like air resistance gradually remove energy from the system, which is why a pendulum's amplitude decreases over time unless an external mechanism restores the lost energy.123