___________ the sum of the kinetic energy and potential energy of a system.

The sum of the kinetic energy and potential energy of a system is called mechanical energy. The mechanical energy of this system is a combination of its kinetic energy and gravitational potential energy. When the pendulum swings back and forth, the kinetic and potential energy are constantly exchanged or converted from one to another but the mechanical energy of the system remains constant. Similarly, when an object is falling on the ground, potential energy is converted into kinetic energy but the total mechanical energy of the system remains the same.