Consider the gravitional interactions among earth, the sun, and the moon. Does this constitute a system? If sure, what are it's boundaries? Is it open or closed? What forms of energy are involved?
Yes, the gravitational interactions among the Earth, the Sun, and the Moon can be considered a system. The boundaries of this system include the interactions between these three celestial bodies, specifically how they interact with each other due to their gravitational forces.
This system can be considered closed as it does not exchange mass or energy with any external environment.
The forms of energy involved in this system include gravitational potential energy, kinetic energy (due to the movement of the Earth, Sun, and Moon), and radiant energy (such as sunlight).