ABSTRACT
This law is often explained by assigning a property to bodies designated as inertia. Since this is a statement about acceleration (change in velocity), and, since acceleration depends on the reference frame with respect to which it is measured, this law is really a statement about reference frames. Reference frames in which this law is valid are called inertial frames. 2
The momentum vector of a body with mass mi is defined as
(4.1-1) where vi is the velocity of the body with respect to an inertial reference frame.
