The appendix is a short primer on concepts referred to in the book.
Newton's laws are all stated in an inertial reference frame, that is, in the frame that moves with no acceleration and no rotation.
Newton's first law. A body continues moving with constant speed in a straight line or stays at rest for as long as the sum of all forces acting on the body is zero.
Newton's second law. Forces applied to a body cause acceleration, and this acceleration a is in direct proportion to the sum of applied forces F:
the coefficient of proportionality m is referred to as the mass. Here a and F are vectors, Figure A.1. Often we look at the projection of Newton's law (A.1) onto a particular direction; for example, when speaking of the rectilinear motion we only care about the direction of the line. In such cases we treat the acceleration and the forces as scalar (as opposed to vector) quantities.