Answer:
Gravitational potential energy to kinetic energy to gravitational potential energy to kinetic energy to gravitational potential energy.
Explanation:
Starting at its maximum displacement the pendulum will have only gravitational potential energy, its velocity being 0m/s. When released, it will lose height, losing then gravitational potential energy as it gains speed, or kinetic energy. When the pendulum is at its lowest the gravitational potential energy will be at its minimum and the kinetic energy at its maximum (and so its speed), with value equal to the original gravitational potential energy. Then it starts gaining height again, reverting this process, gaining gravitational potential energy and losing kinetic energy until the velocity is 0m/s again, thus returning to the state of maximum gravitational potential energy (same as originally) and null kinetic energy, but on the opposite side of the oscillation. Then the pendulum comes back repeating the exact same process just descibed, until it finishes one oscillation when reaching the original point.
