Why do we need to wet the unit of a measurement in the final answer in solving problems
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Answer:
ike all other sciences, physics is based on experimental observations and quan-
titative measurements. The main objective of physics is to find the limited num-
ber of fundamental laws that govern natural phenomena and to use them to
develop theories that can predict the results of future experiments. The funda-
mental laws used in developing theories are expressed in the language of mathe-
matics, the tool that provides a bridge between theory and experiment.
When a discrepancy between theory and experiment arises, new 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) in the 17th century accurately describe the motion of bodies at nor-
mal speeds but do not apply to objects moving at speeds comparable with the
speed of light. In contrast, the special theory of relativity developed by Albert Ein-
stein (1879–1955) in the early 1900s gives the same results as Newton’s laws at low
speeds but also correctly describes motion at speeds approaching the speed of
light. Hence, Einstein’s is a more general theory of motion.
Classical physics, which means all of the physics developed before 1900, in-
cludes the theories, concepts, laws, and experiments in classical mechanics, ther-
modynamics, and electromagnetism.
Important contributions to classical physics were provided by Newton, who de-
veloped classical mechanics as a systematic theory and was 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 electricity and magnetism
were not developed until the latter part of the 19th century, principally because
before that time the apparatus for controlled experiments was either too crude or
unavailable.
A new era in physics, usually referred to as modern physics, began near the end
of the 19th century. Modern physics developed mainly because of the discovery
that many physical phenomena could not be explained by classical physics. The
two most important developments in modern physics were the theories of relativity
and quantum mechanics. Einstein’s theory of relativity revolutionized the tradi-
tional concepts of space, time, and energy; quantum mechanics, which applies to
both the microscopic and macroscopic worlds, was originally formulated by a num-
ber of distinguished scientists to provide descriptions of physical phenomena at
the atomic level.
Scientists constantly work at improving our understanding of phenomena and
fundamental laws, and new discoveries are made every day. In many research
areas, a great deal of overlap exists between physics, chemistry, geology, and
biology, as well as engineering. Some of the most notable developments are
(1) numerous space missions and the landing of astronauts on the Moon,
(2) microcircuitry and high-speed computers, and (3) sophisticated imaging tech-
niques used in scientific research and medicine. The impact such developments
and discoveries have had on our society has indeed been great, and it is very likely
that future discoveries and developments will be just as exciting and challenging
and of great benefit to humanity.
STANDARDS OF LENGTH, MASS, AND TIME
The laws of physics are expressed in terms of basic quantities that require a clear def-
inition. In mechanics, the three basic quantities are length (L), mass (M), and time
(T). All other quantities in mechanics can be expressed in terms of these three.
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