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.