As a branch ofclassical physics, mechanics deals with bodies that are either at rest or are moving with velocities significantly less than the speed of light. It can also be defined as the physical science that deals with the motion of and forces on bodies not in the quantum realm.
There is another tradition that goes back to the ancient Greeks where mathematics is used more extensively to analyze bodiesstatically ordynamically, an approach that may have been stimulated by prior work of the PythagoreanArchytas.[7] Examples of this tradition include pseudo-Euclid (On the Balance),Archimedes (On the Equilibrium of Planes,On Floating Bodies),Hero (Mechanica), andPappus (Collection, Book VIII).[8][9]
In the Middle Ages, Aristotle's theories were criticized and modified by a number of figures, beginning withJohn Philoponus in the 6th century. A central problem was that ofprojectile motion, which was discussed byHipparchus and Philoponus.
Persian Islamic polymathIbn Sīnā published his theory of motion inThe Book of Healing (1020). He said that an impetus is imparted to a projectile by the thrower, and viewed it as persistent, requiring external forces such asair resistance to dissipate it.[10][11][12] Ibn Sina made distinction between 'force' and 'inclination' (called "mayl"), and argued that an object gained mayl when the object is in opposition to its natural motion. So he concluded that continuation of motion is attributed to the inclination that is transferred to the object, and that object will be in motion until the mayl is spent. He also claimed that a projectile in a vacuum would not stop unless it is acted upon, consistent with Newton's first law of motion.[10]
On the question of a body subject to a constant (uniform) force, the 12th-century Jewish-Arab scholarHibat Allah Abu'l-Barakat al-Baghdaadi (born Nathanel, Iraqi, of Baghdad) stated that constant force imparts constant acceleration. According toShlomo Pines, al-Baghdaadi's theory ofmotion was "the oldest negation ofAristotle's fundamental dynamic law [namely, that a constant force produces a uniform motion], [and is thus an] anticipation in a vague fashion of the fundamental law ofclassical mechanics [namely, that a force applied continuously produces acceleration]."[13]
Influenced by earlier writers such as Ibn Sina[12] and al-Baghdaadi,[14] the 14th-century French priestJean Buridan developed thetheory of impetus, which later developed into the modern theories ofinertia,velocity,acceleration andmomentum. This work and others was developed in 14th-century England by theOxford Calculators such asThomas Bradwardine, who studied and formulated various laws regarding falling bodies. The concept that the main properties of a body are uniformly accelerated motion (as of falling bodies) was worked out by the 14th-centuryOxford Calculators.
There is some dispute over priority of various ideas: Newton'sPrincipia is certainly the seminal work and has been tremendously influential, and many of the mathematics results therein could not have been stated earlier without the development of the calculus. However, many of the ideas, particularly as pertain to inertia and falling bodies, had been developed by prior scholars such asChristiaan Huygens and the less-known medieval predecessors. Precise credit is at times difficult or contentious because scientific language and standards of proof changed, so whether medieval statements areequivalent to modern statements orsufficient proof, or insteadsimilar to modern statements andhypotheses is often debatable.
Two main modern developments in mechanics aregeneral relativity ofEinstein, andquantum mechanics, both developed in the 20th century based in part on earlier 19th-century ideas. The development in the modern continuum mechanics, particularly in the areas of elasticity, plasticity, fluid dynamics, electrodynamics, and thermodynamics of deformable media, started in the second half of the 20th century.
Other distinctions between the various sub-disciplines of mechanics concern the nature of the bodies being described. Particles are bodies 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-calleddegrees 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 of study.
For instance, the motion of a spacecraft, regarding itsorbit and attitude (rotation), is described by the relativistic theory of classical mechanics, while the analogous movements of anatomic nucleus are described by quantum mechanics.
The following are the three main designations consisting 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 from mechanics, whether it beclassical fields orquantum fields. But in actual practice, subjects belonging to mechanics and fields are closely interwoven. Thus, for instance, forces that act on particles are frequently derived from fields (electromagnetic orgravitational), and particles generate fields by acting as sources. In fact, in quantum mechanics, particles themselves are fields, as described theoretically by thewave function.
Analytical mechanics is a reformulation of Newtonian mechanics with an emphasis on system energy, rather than on forces. There are two main branches of analytical mechanics:
Historically,classical mechanics had been around for nearly a quarter millennium before quantum mechanics developed. Classical mechanics originated withIsaac Newton'slaws of motion inPhilosophiæ Naturalis Principia Mathematica, developed over the seventeenth century. Quantum mechanics developed later, over the nineteenth century, precipitated byPlanck's postulate and Albert Einstein's explanation of thephotoelectric effect. Both fields 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-calledexact sciences. Essential in this respect is the extensive use ofmathematics in theories, as well as the decisive role played byexperiment in generating and testing them.
Quantum mechanics is of a bigger scope, as it encompasses classical mechanics as a sub-discipline which applies under certain restricted circumstances. According to thecorrespondence 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 quantum theories reproduces classical physics in the limit of largequantum numbers, i.e. if quantum mechanics is applied to large systems (for e.g. a baseball), the result would almost be the same if classical mechanics had been applied. Quantum mechanics has superseded classical mechanics at the foundation level and is indispensable for the explanation and prediction of processes at the molecular, atomic, and sub-atomic level. However, for macroscopic processes classical mechanics is able to solve problems which are unmanageably difficult (mainly due to computational limits) in quantum mechanics and hence remains useful and well used.Modern descriptions of such behavior begin with a careful definition of such 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 scientist Aristotle, scientists reasoned that a cannonball falls down because its natural position is in the Earth; the Sun, the Moon, and the stars travel in circles around the Earth because it is the nature of heavenly objects to travel in perfect circles.
Often cited as father to modern science,Galileo brought together the ideas of other great thinkers of his time and began to calculate motion in terms of distance travelled from some starting position and the time that it took. He showed that the speed of falling objects increases 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 physicistIsaac Newton improved this analysis by defining force and mass and relating these to acceleration. For objects traveling at speeds close to the speed of light, Newton's laws were superseded byAlbert Einstein'stheory of relativity. [A sentence illustrating the computational complication of Einstein's theory of relativity.] For atomic and subatomic particles, Newton's laws were superseded byquantum theory. For everyday phenomena, however, Newton's three laws of motion remain the cornerstone of dynamics, which is the study of what causes motion.
Akin to the distinction between quantum and classical mechanics,Albert Einstein'sgeneral andspecial theories ofrelativity have expanded the scope ofNewton andGalileo's formulation of mechanics. The differences between relativistic and Newtonian mechanics become significant and even dominant as the velocity of a body approaches thespeed of light. For instance, inNewtonian mechanics, thekinetic energy of afree particle isE =1/2mv2, whereas in relativistic mechanics, it isE = (γ − 1)mc2 (whereγ is theLorentz factor; this formula reduces to the Newtonian expression in the low energy limit).[17]
For high-energy processes, quantum mechanics must be adjusted to account for special relativity; this has led to the development ofquantum field theory.[18]
Institution of Mechanical Engineers is the United Kingdom's qualifying body for mechanical engineers and has been the home of Mechanical Engineers for over 150 years.
International Union of Theoretical and Applied Mechanics
^Henry George Liddell; Robert Scott (1940)."mechanics".A Greek-English Lexicon.
^Young, Hugh D.; Roger A. Freedman; A. Lewis Ford; Katarzyna Zulteta Estrugo (2020).Sears and Zemansky's university physics: with modern physics (15th ed.). Harlow: Pearson Education. p. 62.ISBN978-1-292-31473-0.OCLC1104689918.
^Dugas, Rene. A History of Classical Mechanics. New York, NY: Dover Publications Inc, 1988, pg 19.
^Rana, N.C., and Joag, P.S. Classical Mechanics. West Petal Nagar, New Delhi. Tata McGraw-Hill, 1991, pg 6.
^Renn, J., Damerow, P., and McLaughlin, P. Aristotle, Archimedes, Euclid, and the Origin of Mechanics: The Perspective of Historical Epistemology. Berlin: Max Planck Institute for the History of Science, 2010, pg 1-2.
^Pines, Shlomo (1970). "Abu'l-Barakāt al-Baghdādī , Hibat Allah".Dictionary of Scientific Biography. Vol. 1. New York: Charles Scribner's Sons. pp. 26–28.ISBN0-684-10114-9. (cf. Abel B. Franco (October 2003). "Avempace, Projectile Motion, and Impetus Theory",Journal of the History of Ideas64 (4), p. 521-546 [528].)
