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الثلاثاء، 9 سبتمبر، 2014



Like all other sciences, physics is based on experimental observations and quantitative
measurements. The main objectives of physics are to identify a limited number of fundamental
laws that govern natural phenomena and use them to develop theories that can predict
the results of future experiments. The fundamental laws used in developing theories are
expressed in the language of mathematics, the tool that provides a bridge between theory
and experiment.
When there is a discrepancy between the prediction of a theory and experimental
results, new or modified theories must be formulated to remove the discrepancy. Many
times a theory is satisfactory only under limited conditions; a more general theory might be
satisfactory without such limitations. For example, the laws of motion discovered by Isaac
Newton (1642–1727) accurately describe the motion of objects moving at normal speeds but
do not apply to objects moving at speeds comparable to the speed of light. In contrast, the
special theory of relativity developed later by Albert Einstein (1879–1955) gives the same
results as Newton’s laws at low speeds but also correctly describes the motion of objects at
speeds approaching the speed of light. Hence, Einstein’s special theory of relativity is a more
general theory of motion than that formed from Newton’s laws.
Classical physics includes the principles of classical mechanics, thermodynamics, optics,
and electromagnetism developed before 1900. Important contributions to classical physics were provided by Newton, who was also one of the originators of calculus as a mathematical
tool. Major developments in mechanics continued in the 18th century, but the fields of
thermodynamics and electromagnetism were not developed until the latter part of the 19th
century, principally because before that time the apparatus for controlled experiments in
these disciplines was either too crude or unavailable.
A major revolution in physics, usually referred to as modern physics, began near the end
of the 19th century. Modern physics developed mainly because many physical phenomena
could not be explained by classical physics. The two most important developments in this
modern era were the theories of relativity and quantum mechanics. Einstein’s special theory
of relativity not only correctly describes the motion of objects moving at speeds comparable
to the speed of light; it also completely modifies the traditional concepts of space,
time, and energy. The theory also shows that the speed of light is the upper limit of the
speed of an object and that mass and energy are related. Quantum mechanics was formulated
by a number of distinguished scientists to provide descriptions of physical phenomena
at the atomic level. Many practical devices have been developed using the principles of
quantum mechanics.
Scientists continually work at improving our understanding of fundamental laws.
Numerous technological advances in recent times are the result of the efforts of many
scientists, engineers, and technicians, such as unmanned planetary explorations, a variety
of developments and potential applications in nanotechnology, microcircuitry and
high-speed computers, sophisticated imaging techniques used in scientific research and
medicine, and several remarkable results in genetic engineering. The effects of such developments
and discoveries on our society have indeed been great, and it is very likely that
future discoveries and developments will be exciting, challenging, and of great benefit to

الاثنين، 8 سبتمبر، 2014

Introduction - physics equations


Physics, the most fundamental physical science, is concerned with the fundamental
principles of the Universe. It is the foundation upon which the other sciences—astronomy,
biology, chemistry, and geology—are based. It is also the basis of a large number of engineering
applications. The beauty of physics lies in the simplicity of its fundamental principles and in the
manner in which just a small number of concepts and models can alter and expand our view of the
world around us.
T he study of physics can be divided into six main areas:
1. classical mechanics, concerning the motion of objects that are large relative to atoms and
move at speeds much slower than the speed of light
2. relativity, a theory describing objects moving at any speed, even speeds approaching the
speed of light
3. thermodynamics, dealing with heat, work, temperature, and the statistical behavior of systems
with large numbers of particles
4. electromagnetism, concerning electricity, magnetism, and electromagnetic fields
5. optics, the study of the behavior of light and its interaction with materials
6. quantum mechanics, a collection of theories connecting the behavior of matter at the submicroscopic
level to macroscopic observations
The disciplines of mechanics and electromagnetism are basic to all other branches of classical physics
(developed before 1900) and modern physics (c. 1900–present). The first part of this textbook deals
with classical mechanics, sometimes referred to as Newtonian mechanics or simply mechanics. Many
principles and models used to understand mechanical systems retain their importance in the theories
of other areas of physics and can later be used to describe many natural phenomena. Therefore,
classical mechanics is of vital importance to students from all disciplines.