(Please forgive me for the obvious stupidity of this question) I'm trying to understand Newton's laws down to the last detail, because that is how I study things. However, where would the principle of inertia ever take place? And since Newton's laws are only applicable in an inertia frame reference, are the laws correct? How would an object in motion going at its constant velocity without any "forces" get in motion in a frame of inertia without an initial force? Does it mean that it was in a place that started it's one initial push of force then it entered a place with no forces, where it would continue on forever? Thank you for any answers in advance.