Re: How the moon was formed?
At any point of formation, from the moment the dust starts swirling around to the moment a rock solid planet is formed. Collisions are common! Maybe not as big as Mars crashing into the earth but big and small collisions are quite frequent. Not frequent enough for our civilization to witness them though.
Ah I think I know why we are confused. We are thinking of different things when we say “collisions.”
Do you mean colliding with another object that’s in its own orbit or tidally locked with another celestial body? If that’s what you are talking about then yes, it’s not common at all or we would be able to observe it or at least know that another gravitational force exists around us.