Consider the gravitational interactions among the earth, the sun ,and the moon. Does this constitute a system? If so what are its boundaries? Is it open or close?what forms of energy are involved?
Yes, the gravitational interactions among the earth, the sun, and the moon constitute a system. The boundaries of this system would be the gravitational field surrounding these three celestial bodies. This system is considered open because energy (in the form of gravitational potential energy) and momentum can be transferred into or out of the system.
The forms of energy involved in this system are gravitational potential energy, as well as kinetic energy due to the motion of the bodies in their orbits. Additionally, electromagnetic radiation in the form of sunlight is also a form of energy present in this system.