Newton’ s First lay An object subject to no external forces moves with a constant velocity if viewed from an inertial reference frame If no forces act there is no acceleration The above statement can be thought of as the definition of inertial reference frames An IRF is a reference frame that is not accelerating(or rotating) with respect to the fixed stars If one IRF exists, infinitely many exist since they are related by any arbitrary constant velocity vector Physics 121: Lecture 7, Pg 11Physics 121: Lecture 7, Pg 11 Newton’s First Law An object subject to no external forces moves with a constant velocity if viewed from an inertial reference frame. If no forces act, there is no acceleration. The above statement can be thought of as the definition of inertial reference frames. An IRF is a reference frame that is not accelerating (or rotating) with respect to the “fixed stars”. If one IRF exists, infinitely many exist since they are related by any arbitrary constant velocity vector!