ABSTRACT
The aim of this chapter is to present some very basic principles
of classical mechanics. They can help us understand the novelty of
quantum theory.
Classical mechanics was founded by Newton and contemporary
17th-century natural philosophers, and further developed in the
18th and 19th centuries by many physicists and mathematicians, as
a result of the search for a rational, causal, and scientific explanation
of the universe. In classical mechanics, real-world objects are
modeled as a collection of point particles, i.e., objects with negligible
size. The motion of a point particle is characterized by a small
number of parameters such as its position, mass, velocity, and the
forces applied to it. The position of a point particle is defined
with respect to an arbitrary fixed reference point in the three-
dimensional Euclidean space, which is usually chosen as the origin
of some coordinate system. The velocity of a point particle is the
rate of change of its position with time. The force applied to a point
particle (called the external force) is the cause for the point particle
x
y
z
A
to undergo a certain change in its velocity, i.e., an acceleration
(Newton’s second law of motion). For the sake of simplicity, here
we shall refer to a point particle or a collection of point particles
simply as an object. Newton’s first law of motion states that if an
object experiences no net external force, then its velocity is constant,
i.e., the object is either at rest or it moves in a straight line with a
constant speed. The first law of motion postulates the existence of a
certain set of frames of reference called inertial reference frames,
relative to which the motion of an object not subject to external
forces is a straight line at a constant speed. For this reason, Newton’s
first law is also referred to as the law of inertia.