In: Mechanical Engineering
i have to write a survey paper on the history of a dynamics related concept, tool, application, or mechanism. i am struggling to find good topics. please help me by suggesting some topics
This article describes a few key points in the development of
the field of dynamics. It begins with a brief overview of dynamics’
origins in Ancient Greece, and progresses through the Middle {Ages
and the Renaissance, stopping at the times, places, and people that
the author considers most relevant. Following that, it summarises
the appearance of the Principia, and proceeds to explain its
development into what we now call Classical Mechanics.
It should be clear that the contents are not new: they are well
known in many fields and have been for many years. They are
presented to the control community in the hope that knowledge of,
and interest in, the history of science might be improved. Any
contributions solely in bringing the subject to an audience that is
perhaps generally unacquainted with it. Not only are the contents
not new, they are also by no means complete or comprehensive. With
those caveats, the author hopes that some of the intended audience
might find value in what is presented.
Newton discovered universal gravitation and completed the formal
enunciation of the mechanical principles now generally accepted.
Since his time no essentially new principle has been stated. All
that has been accomplished in mechanics since his day has been a
deductive, formal, and mathematical development of mechanics on the
basis of Newton’s Laws.
The sentiments expressed by Mach are broadly in line with the
opinions of many in academia. The popularity of a belief does not
allow us to conclude whether
it is factual or not.
The motivation for writing this paper stems from the sentiments of
the great physicist, mathematician, historian of science, and
polemicist, Clifford Truesdell2. In his essay A Program
toward Rediscovering the Rational Mechanics of the Age of
Reason, he wrote:
The scientists, in so far as they take any note of history at all, not only have shared the historians’ neglect of the later [i.e., after Newton] mathematical development of mechanics but also, in the main, have ignored what the historians have learned about the earlier periods and have rested content with Mach’s whole view or a rudimentary abstract of it.
Whether reading a textbook on robotics, marine engineering,
aerospace engineering or, indeed, on mechanics itself, the
statement above is too often applicable. Discussions of dynamics
almost invariably begin by citing the work of Newton (1687) in his
Principia, and seldom proceed further than this opus. It is as if
classical mechanics arose from the genius of Newton alone.
This hagiography does a great disservice to at least four parties:
firstly, to the scholars whose works predate Newton; secondly, to
Newton’s contemporaries and successors, who actually synthesised
the dynamics that we know and apply today; thirdly, to the present
{day students who desire an accurate history of dynamics; and
fourthly to Newton himself, whose memory is sullied by the
misrepresentation of his work.
This neglect leads us to question why this history is being
contemplated here. The problem is that the history of science, a
large and growing field, seems to filter little of its knowledge to
the practitioners of science. Scientific careers can be built on
advanced topics with absolutely no concept of what lies in the
foundations. The history of a science is vital to a humble
understanding of that science.
Awkwardly, the history of a science can only really be grasped and
analyzed after the subject itself is sufficiently well understood.
However, once that science is understood and a university degree
comes to its end, there is no drive to put the learning into a
historical perspective. A modern engineering degree is then more
like an advanced trade school diploma than the higher form of
learning and understanding that it ought to be, and that it used to
be.
A cursory and often inaccurate glance at history seems sufficient
nowadays, but should it be? The development of dynamics is a much
longer, halting and laborious story that neither began nor ended
with Isaac Newton.
Sir Isaac Newton
Sir Isaac Newton (1643-1728), made contributions to virtually
every area of natural
philosophy, mathematics, optics, and astronomy. His monumental
publication, Philosophy Naturalis Principia Mathematica, usually
called The Principia in short, was published in 1687. It is likely
the most influential book in the field of classical mechanics, yet
is little read. Its purpose was set forth in its preface:
...mechanics will be the science of motion
resulting from any forces whatsoever, and of
the forces required to produce any motion...
Newton set out to explain phenomena throughout the universe. What
lay within was to apply everywhere and to every process. The
trajectory taken by a cannonball was to be governed by the same
laws which governed the orbits of the planets. As the start of his
work, he states his definitions of mass, momentum, inertia, and
forces, both through contact and at a distance. He then states his
laws:
First Law
Everybody perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed upon it thereon.
Second Law The alteration of motion is
proportional to the motive force impressed and is made in the
direction of the right line in which that force is impressed.
Third Law To every action there is always opposed
an equal reaction: or the mutual actions of two bodies upon each
other are always equal, and directed to contrary parts.
It is broadly divided into three books, each of which alone would
eclipse almost any other. Books One and Two are titled Of the
Motion of Bodies, being split into two exhaustive analyses. The
third is titled The System of the World.The first book analyses
motions in a void. From his laws, he analyses a multitude of
motions, such as elliptic, parabolic and hyperbolic orbits around
some focus.He investigates the forces that maintain these, i.e. the
centripetal forces. Universal gravitation is introduced. After
showing how point masses behave in the void under gravitation, he
demonstrates that finite bodies can be treated as such. Kepler’s
Laws follow directly.The first book organized and systematized
principles,
some of which were at least dimly understood before, but these
principles had never been organized together into a system of
analysis for application everywhere.The second book sets out to
explain motion on Earth, where motion does not occur in a void: he
sought the details of motion in resisting media. It is here that
Newton departs from his program of deducing physical behavior based
on his laws: he finds but little use for them. For example, in all
his treatments of fluidic motion, he finds no room to apply his
principle of momentum. In contrast, he conjures ingenious
hypotheses to explain a myriad of things ranging from projectile
motions to the speed of sound in air. This book is a testament to
Newton’s towering stature as a mathematician and dynamicist. The
second book of the Principia is almost entirely new. The scholium
of the first section of it reads:
But, yet, that the resistance of bodies is in
the ratio of the velocity, is more a mathematical hypothesis than a
physical one.
This sentiment is applicable to much of the hypotheses in the
book. Today it is mostly forgotten. The book is dominated by
hypothesis after hypothesis, with Newton displaying his flair for
creative solutions: often precise, often an excellent
approximation, but also often wrong and today of only historical
value. There are veins of gold hidden within. His observation that
fluidic resistance is proportional to the square of velocity can be
found, as can the first description of internal fluidic
friction:
The resistance arising from the want of
lubricity in the parts of a fluid is, cæteris
paribus, proportional to the velocity with
which the parts of the fluid are separated from
each other.
That most of the results were incorrect cannot be a criticism of
Newton either as a physicist or mathematician. The contribution of
this book is immeasurable. For instance, it constitutes the
beginning of fluid dynamics and studied many of its problems for
the first time. From his efforts, his contemporaries and successors
were gifted with a bridgehead from which to attack these subjects
in earnest. A myriad of potential motions through fluids is
contemplated. The book is the staging point for hydrodynamics.
Newton contemplated which hull form might pass through the water
with least resistance, introducing an optimization problem that
found application throughout the 19thcentury.
The third book set forth his solutions to problems in celestial
dynamics, with great success. Kepler’s Laws of Planetary Motion had
resulted from Newton’s own, and he performed exhaustive analyses of
the Solar System. The deficiencies in the Principia are little
discussed.
To the modern scholar, it is often impenetrable and confusing; the
language of mathematics has evolved so much since then. A common
remark made about the Principia is that Newton strangely resorts to
geometrical methods instead of his own calculus. Newton does not
use his notation of fluxions, but even as soon as we arrive at
Lemma II of Book I, the notion of calculus is present, if in an
unfamiliar form.
For rigid body mechanics, there is no treatment of rotation.
Although Newton says that the spinning top does not stop spinning
except insofar as it is slowed by air." there is no justification
given. His statement appears directly after his statement of the
First Law, but this law cannot tell us anything about the spinning
top. Newton might have perceived that the top continues topspin,
just as it would continue in linear motion if so impelled, but it
is not possible to explain the spinning top using what is within
the Principia. There is certainly no treatment of angular momentum.
The motion of a rigid body cannot be described by the methods given
in the Principia.
There is no treatment of flexible bodies, such as the catenary
curve or the vibrating string, nor is there any analysis of the
finite body pendulum. No equations of motion appear for systems of
more than two free masses, or one constrained. A prime example of
the field’s infancy is the three{body problem. Newton attempted to
solve this problem, but the contents of the Principia are
insufficient to do so. He devised insightful approximations and
valid inequalities, but the three{ body problem was insoluble from
his principles. His talent in this area is evident, as his work
would not be surpassed until the mid{18th century by the efforts of
Euler and Lagrange.
That Newton did not solve all of mechanics’ problems is not a
criticism at all, but only part of a clear{ headed appraisal of
what he did do. His achievements were monumental. He ought not to
be credited with the completion of classical mechanics, but rather
its beginnings. In the century following The Principia’s
publication, the field of mechanics swelled immensely. For all the
credit given to Newton, the world ought to be equally
grateful to his contemporaries and successors, especially Leonhard
Euler, the Bernoullis Jakob and John, and Joseph Lagrange. These
are the men who synthesized what we now apply today.