- An inertial reference frames is a reference frame on which there is no net external force.
- A frame moving with constant velocity is an inertial reference frame.
- But a frame with non-zero acceleration is not an inertial reference frame.
- So Earth is technically not an inertial reference frame since rotation results in change of velocity ⇒ accelerating. But the effects are negligible.
- Newton’s Laws of Motion are true only in inertial reference frames.