What is the reasoning of the energy changes that occur while the pendulum is in motion.

As a pendulum swings, its potential energy converts to kinetic and back to potential. Recall the concept of conservation of energy—that energy may change its form, but have no net change to the amount of energy.

Explanation:

At every point in the motion of the pendulum the total mechanical energy is conserved. The sum of the gravitational potential energy and the kinetic energy, at each point of the motion, is a constant, which is the total mechanical energy. A pendulum is a simple example of energy transfer. ... When it is allowed to swing, that energy is gradually converted to energy of motion – kinetic energy. When the pendulum is at position B, all of its potential energy has been converted to kinetic energy and it is moving at its maximum speed.

the dependant variable is spilled water

the independent is the heat