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Mechanics
Mechanics (Greek μηχανική) is an area of science concerned with the behaviour of physical bodies when subjected to forces or
displacements, and the subsequent effects of the bodies on their environment. The scientific discipline has its origins in Ancient
Greece with the writings of Aristotle and Archimedes[1][2][3] (see History of classical mechanics and Timeline of classical
mechanics). During the early modern period, scientists such as Galileo, Kepler, and Newton, laid the foundatio

Mechanics
Mechanics
(Greek μηχανική) is an area of science concerned with the behaviour of physical bodies when subjected to forces ordisplacements, and the subsequent effects of the bodies on their environment. The scientific discipline has its srcins in AncientGreece with the writings of Aristotle and Archimedes
[1][2][3]
(see History of classical mechanics and Timeline of classicalmechanics). During the early modern period, scientists such as Galileo, Kepler, and Newton, laid the foundation for what is nowknown as classical mechanics. It is a branch of classical physics that deals with particles that are either at rest or are moving with
velocities significantly less than the speed of light. It can also be defined as a branch of science which deals with the motion of and
forces on objects.
Cla ssical versus quantumRelativistic versus NewtonianGeneral relativistic versus quantumHistory
AntiquityMedieval ageEarly modern ageModern age
Types of mechanical bodiesSub - disciplines
ClassicalQuantum
Professional organizationsSee alsoReferencesFurther readingExternal links
Historically, classical mechanics came first, while quantum mechanics is a comparatively recent invention. Classical mechanicssrcinated with Isaac Newton's laws of motion in Philosophiæ Naturalis Principia Mathematica; Quantum Mechanics was discoveredin the early 20th century. Both are commonly held to constitute the most certain knowledge that exists about physical nature.Classical mechanics has especially often been viewed as a model for other so-called exact sciences. Essential in this respect is theextensive use of mathematics in theories, as well as the decisive role played by experiment in generating and testing them.Quantum mechanics is of a bigger scope, as it encompasses classical mechanics as a sub-discipline which applies under certainrestricted circumstances. According to the correspondence principle, there is no contradiction or conflict between the two subjects,each simply pertains to specific situations. The correspondence principle states that the behavior of systems described by quantumtheories reproduces classical physics in the limit of large quantum numbers. Quantum mechanics has superseded classical mechanicsat the foundation level and is indispensable for the explanation and prediction of processes at the molecular, atomic, and sub-atomiclevel. However, for macroscopic processes classical mechanics is able to solve problems which are unmanageably difficult in
ContentsClassical versus quantum
quantum mechanics and hence remains useful and well used. Modern descriptions of such behavior begin with a careful definition ofsuch quantities as displacement (distance moved), time, velocity, acceleration, mass, and force. Until about 400 years ago, however,motion was explained from a very different point of view. For example, following the ideas of Greek philosopher and scientistAristotle, scientists reasoned that a cannonball falls down because its natural position is in the Earth; the sun, the moon, and the starstravel in circles around the earth because it is the nature of heavenly objects to travel in perfect circles.Often cited as the father of modern science, Galileo brought together the ideas of other great thinkers of his time and began to analyzemotion in terms of distance traveled from some starting position and the time that it took. He showed that the speed of falling objectsincreases steadily during the time of their fall. This acceleration is the same for heavy objects as for light ones, provided air friction(air resistance) is discounted. The English mathematician and physicist Isaac Newton improved this analysis by defining force andmass and relating these to acceleration. For objects traveling at speeds close to the speed of light, Newton’s laws were superseded byAlbert Einstein’s theory of relativity. For atomic and subatomic particles, Newton’s laws were superseded by quantum theory. Foreveryday phenomena, however, Newton’s three laws of motion remain the cornerstone of dynamics, which is the study of whatcauses motion.In analogy to the distinction between quantum and classical mechanics, Einstein's general and special theories of relativity haveexpanded the scope of Newton and Galileo's formulation of mechanics. The differences between relativistic and Newtonianmechanics become significant and even dominant as the velocity of a massive body approaches the speed of light. For instance, inNewtonian mechanics, Newton's laws of motionspecify that
F
=
m
a
, whereas in Relativistic mechanicsand Lorentz transformations,which were first discovered by Hendrik Lorentz,
F
= γ
m
a
(where γ is the Lorentz factor, which is almost equal to 1 for low speeds).Relativistic corrections are also needed for quantum mechanics, although general relativity has not been integrated. The two theoriesremain incompatible, a hurdle which must be overcome in developing a theory of everything.The main theory of mechanics in antiquity was Aristotelian mechanics.
[4]
A later developer in this tradition is Hipparchus.
[5]
In the Middle Ages, Aristotle's theories were criticized and modified by a number of figures, beginning with John Philoponus in the6th century. A central problem was that of projectile motion, which was discussed by Hipparchus and Philoponus. This led to thedevelopment of the theory of impetus by 14th-century French priest Jean Buridan, which developed into the modern theories ofinertia, velocity, acceleration and momentum. This work and others was developed in 14th-century England by the OxfordCalculators such as Thomas Bradwardine, who studied and formulated various laws regarding falling bodies.On the question of a body subject to a constant (uniform) force, the 12th-century Jewish-Arab Nathanel (Iraqi, of Baghdad) statedthat constant force imparts constant acceleration, while the main properties are uniformly accelerated motion (as of falling bodies)was worked out by the 14th-century Oxford Calculators.
Relativistic versus NewtonianGeneral relativistic versus quantumHistory
AntiquityMedieval ageEarly modern age
Two central figures in the early modern age are Galileo Galilei and Isaac Newton.Galileo's final statement of his mechanics, particularly of falling bodies, is his
Two NewSciences
(1638). Newton's 1687
Philosophiæ Naturalis Principia Mathematica
provideda detailed mathematical account of mechanics, using the newly developed mathematicsof calculus and providing the basis of Newtonian mechanics.
[5]
There is some dispute over priority of various ideas: Newton's
Principia
is certainly theseminal work and has been tremendously influential, and the systematic mathematicstherein did not and could not have been stated earlier because calculus had not beendeveloped. However, many of the ideas, particularly as pertain to inertia (impetus) andfalling bodies had been developed and stated by earlier researchers, both the then-recentGalileo and the less-known medieval predecessors. Precise credit is at times difficult orcontentious because scientific language and standards of proof changed, so whethermedieval statements are
equivalent
to modern statements or
sufficient
proof, or instead
similar
to modern statements and
hypotheses
is often debatable.Two main modern developments in mechanics are general relativity of Einstein, andquantum mechanics, both developed in the 20th century based in part on earlier 19th-century ideas. The development in the moderncontinuum mechanics, particularly in the areas of elasticity, plasticity, fluid dynamics, electrodynamics and thermodynamics ofdeformable media, started in the second half of the 20th century.The often-used term
body
needs to stand for a wide assortment of objects, including particles, projectiles, spacecraft, stars, parts ofmachinery, parts of solids, parts of fluids (gases and liquids), etc.Other distinctions between the various sub-disciplines of mechanics, concern the nature of the bodies being described. Particles arebodies with little (known) internal structure, treated as mathematical points in classical mechanics. Rigid bodies have size and shape,but retain a simplicity close to that of the particle, adding just a few so-called degrees of freedom, such as orientation in space.Otherwise, bodies may be semi-rigid, i.e. elastic, or non-rigid, i.e. fluid. These subjects have both classical and quantum divisions ofstudy.For instance, the motion of a spacecraft, regarding its orbit and attitude (rotation), is described by the relativistic theory of classicalmechanics, while the analogous movements of an atomic nucleus are described by quantum mechanics.The following are two lists of various subjects that are studied in mechanics.Note that there is also the theory of fields which constitutes a separate discipline in physics, formally treated as distinct frommechanics, whether classical fields or quantum fields. But in actual practice, subjects belonging to mechanics and fields are closelyinterwoven. Thus, for instance, forces that act on particles are frequently derived from fields (electromagnetic or gravitational), andparticles generate fields by acting as sources. In fact, in quantum mechanics, particles themselves are fields, as described theoreticallyby the wave function.The following are described as forming classical mechanics:
Arabic Machine Manuscript.Unknown date (at a guess: 16thto 19th centuries).
Modern age
Types of mechanical bodiesSub - disciplines
Classical
Newtonian mechanics, the srcinal theory of motion (kinematics) andforces (dynamics).Analytical mechanicsis a reformulation of Newtonian mechanics with anemphasis on system energy, rather than on forces. There are two mainbranches of analytical mechanics:Hamiltonian mechanics, a theoretical formalism, based on theprinciple of conservation of energy.Lagrangian mechanics, another theoretical formalism, based on theprinciple of the least action.Classical statistical mechanicsgeneralizes ordinary classical mechanicsto consider systems in an unknown state; often used to derivethermodynamic properties.Celestial mechanics, the motion of bodies in space: planets, comets,stars, galaxies, etc.Astrodynamics, spacecraft navigation, etc.Solid mechanics, elasticity, plasticity, viscoelasticity exhibited bydeformable solids.Fracture mechanicsAcoustics, sound ( = density variation propagation) in solids, fluids and gases.Statics, semi-rigid bodies in mechanical equilibriumFluid mechanics, the motion of fluidsSoil mechanics, mechanical behavior of soilsContinuum mechanics, mechanics of continua (both solid and fluid)Hydraulics, mechanical properties of liquidsFluid statics, liquids in equilibriumApplied mechanics, or Engineering mechanicsBiomechanics, solids, fluids, etc. in biologyBiophysics, physical processes in living organismsRelativistic or Einsteinian mechanics, universal gravitation.
The following are categorized as being part of quantum mechanics:
Schrödinger wave mechanics, used to describe the movements of the wavefunction of a single particle.Matrix mechanics is an alternative formulation that allows considering systems with a finite-dimensional state space.Quantum statistical mechanicsgeneralizes ordinary quantum mechanics to consider systems in an unknown state;often used to derive thermodynamic properties.Particle physics, the motion, structure, and reactions of particlesNuclear physics, the motion, structure, and reactions of nucleiCondensed matter physics, quantum gases, solids, liquids, etc.Applied Mechanics Division, American Society of Mechanical EngineersFluid Dynamics Division, American Physical SocietySociety for Experimental MechanicsInstitution of Mechanical Engineersis the United Kingdom's qualifying body for Mechanical Engineers and has beenthe home of Mechanical Engineers for over 150 years.International Union of Theoretical and Applied MechanicsApplied mechanicsDynamicsEngineeringProf. Walter Lewin explains Newton'slaw of gravitation in MIT course8.01
[6]
Play media
Quantum
Professional organizationsSee also

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