# Homework Help: Where is the intertial frame of reference applicable?

1. Jun 1, 2013

(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.

2. Jun 1, 2013

### Staff: Mentor

Welcome to Physics Forums.

The inertial frame of reference refers to that of the observer, not to the object. It is the observer who has no forces acting on him. He can use his inertial frame of reference coordinate system to quantify the kinematics of the object's motion, and to apply Newton's laws. Another observer from another inertial frame of reference can do the same, and still have Newton's laws properly apply in his frame of reference. This is how the principle of inertia works.

3. Jun 1, 2013

Where would an observer have no forces acting upon him? How is it used to quantify the kinematics?

Thank you for your patience.

4. Jun 1, 2013