Consider the gravitational interactions among Earth, the sun and the moon. Does this constitute a system? If so, what are its boundaries? It is open or closed and what forms of energy are involved?
Yes, the gravitational interactions among Earth, the sun, and the moon constitute a system. The boundaries of this system would include the Earth, sun, and moon themselves, as well as the space in which they interact.
This system is considered closed, as there is no exchange of matter with external sources. Energy forms involved in this system include gravitational potential energy, kinetic energy, and electromagnetic energy (from the sun). Additionally, the system also involves rotational and orbital energy.