Who identified force in physics?
George Berkeley
Berkeley argued that forces and gravity, as defined by Newton, constituted "occult qualities" that "expressed nothing distinctly". He held that those who posited "something unknown in a body of which they have no idea and which they call the principle of motion, are in fact simply stating that the principle of motion is unknown." Therefore, those who "affirm that active force, action, and the principle of motion are really in bodies are adopting an opinion not based on experience." Forces and gravity existed nowhere in the phenomenal world. On the other hand, if they resided in the category of "soul" or "incorporeal thing", they "do not properly belong to physics" as a matter. Berkeley thus concluded that forces lay beyond any kind of empirical observation and could not be a part of proper science. He proposed his theory of signs as a means to explain motion and matter without reference to the "occult qualities" of force and gravity.
Louis Poinsot
Louis Poinsot (3 January 1777 – 5 December 1859) was a French mathematician and physicist. Poinsot was the inventor of geometrical mechanics, showing how a system of forces acting on a rigid body could be resolved into a single force and a couple.
History of physics
In 1739, Leonhard Euler solved the ordinary differential equation for a forced harmonic oscillator and noticed the resonance phenomenon. In 1742, Colin Maclaurin discovered his uniformly rotating self-gravitating spheroids. In 1742, Benjamin Robins published his "New Principles in Gunnery", establishing the science of aerodynamics. British work, carried on by mathematicians such as Taylor and Maclaurin, fell behind Continental developments as the century progressed. Meanwhile, work flourished at scientific academies on the Continent, led by such mathematicians as Bernoulli, Euler, Lagrange, Laplace, and Legendre. In 1743, Jean le Rond d'Alembert published his "Traite de Dynamique", in which he introduced the concept of generalized forces for accelerating systems and systems with constraints, and applied the new idea of virtual work to solve dynamical problem, now known as D'Alembert's principle, as a rival to Newton's second law of motion. In 1747, Pierre Louis Maupertuis applied minimum principles to mechanics. In 1759, Euler solved the partial differential equation for the vibration of a rectangular drum. In 1764, Euler examined the partial differential equation for the vibration of a circular drum and found one of the Bessel function solutions. In 1776, John Smeaton published a paper on experiments relating power, work, momentum and kinetic energy, and supporting the conservation of energy. In 1788, Joseph Louis Lagrange presented Lagrange's equations of motion in "Mécanique Analytique", in which the whole of mechanics was organized around the principle of virtual work. In 1789, Antoine Lavoisier states the law of conservation of mass. The rational mechanics developed in the 18th century received a brilliant exposition in both Lagrange's 1788 work and the "Celestial Mechanics" (1799–1825) of Pierre-Simon Laplace.
Aristotelian physics
In 1121, al-Khazini, in "The Book of the Balance of Wisdom", proposed that the gravity and gravitational potential energy of a body varies depending on its distance from the centre of the Earth. Hibat Allah Abu'l-Barakat al-Baghdaadi (1080–1165) wrote "al-Mu'tabar", a critique of Aristotelian physics where he negated Aristotle's idea that a constant force produces uniform motion, as he realized that a force applied continuously produces acceleration, a fundamental law of classical mechanics and an early foreshadowing of Newton's second law of motion. Like Newton, he described acceleration as the rate of change of speed.
Fifth force
In physics, there are four conventionally accepted fundamental forces or interactions that form the basis of all known interactions in nature: gravitational, electromagnetic, strong nuclear, and weak nuclear forces.
Some speculative theories have proposed a fifth force to explain various anomalous observations that do not fit existing theories. The characteristics of this fifth force depend on the theory being advanced. Many postulate a force roughly the strength of gravity (i.e. it is much weaker than electromagnetism or the nuclear forces) with a range of anywhere from less than a millimeter to cosmological scales. Another proposal is a new weak force, mediated by W' and Z' bosons.
Torque
The term "torque" was introduced into English scientific literature by James Thomson, the brother of Lord Kelvin, in 1884. However, torque is referred to using different vocabulary depending on geographical location and field of study. This article refers to the definition used in US physics in its usage of the word "torque". In the UK and in US mechanical engineering, torque is referred to as "moment of force", usually shortened to "moment". In US physics and UK physics terminology these terms are interchangeable, unlike in US mechanical engineering, where the term "torque" is used for the closely related "resultant moment of a couple".
Space physics
Space physics can be traced to the Chinese who discovered the principle of the compass, but did not understand how it worked. During the 16th century, in "De Magnete", William Gilbert gave the first description of the Earth's magnetic field, showing that the Earth itself is a great magnet, which explained why a compass needle points north. Deviations of the compass needle magnetic declination were recorded on navigation charts, and a detailed study of the declination near London by watchmaker George Graham resulted in the discovery of irregular magnetic fluctuations that we now call magnetic storms, so named by Alexander Von Humboldt. Gauss and William Weber made very careful measurements of Earth's magnetic field which showed systematic variations and random fluctuations. This suggested that the Earth was not an isolated body, but was influenced by external forces – especially from the Sun and the appearance of sunspots. A relationship between individual aurora and accompanying geomagnetic disturbances was noticed by Anders Celsius and Olof Peter Hiorter in 1747. In 1860, Elias Loomis (1811–1889) showed that the highest incidence of aurora is seen inside an oval of 20 - 25 degrees around the magnetic pole. In 1881, Hermann Fritz published a map of the "isochasms" or lines of constant magnetic field.
Quantum field theory
The earliest successful classical field theory is one that emerged from Newton's law of universal gravitation, despite the complete absence of the concept of fields from his 1687 treatise "Philosophiæ Naturalis Principia Mathematica". The force of gravity as described by Newton is an "action at a distance" — its effects on faraway objects are instantaneous, no matter the distance. In an exchange of letters with Richard Bentley, however, Newton stated that "it is inconceivable that inanimate brute matter should, without the mediation of something else which is not material, operate upon and affect other matter without mutual contact." It was not until the 18th century that mathematical physicists discovered a convenient description of gravity based on fields — a numerical quantity (a vector (mathematics and physics)) assigned to every point in space indicating the action of gravity on any particle at that point. However, this was considered merely a mathematical trick.
Statics
Force is the action of one body on another. A force is either a push or a pull. A force tends to move a body in the direction of its action. The action of a force is characterized by its magnitude, by the direction of its action, and by its point of application. Thus, force is a vector quantity, because its effect depends on the direction as well as on the magnitude of the action.
Hooke's law
Hooke's law is a law of physics that states that the force () needed to extend or compress a spring by some distance scales linearly with respect to that distance. That is: formula_1, where is a constant factor characteristic of the spring: its stiffness, and is small compared to the total possible deformation of the spring. The law is named after 17th-century British physicist Robert Hooke. He first stated the law in 1676 as a Latin anagram. He published the solution of his anagram in 1678 as: "ut tensio, sic vis" ("as the extension, so the force" or "the extension is proportional to the force"). Hooke states in the 1678 work that he was aware of the law already in 1660.
AdS/CFT correspondence
Current understanding of gravity is based on Albert Einstein's general theory of relativity. Formulated in 1915, general relativity explains gravity in terms of the geometry of space and time, or spacetime. It is formulated in the language of classical physics developed by physicists such as Isaac Newton and James Clerk Maxwell. The other nongravitational forces are explained in the framework of quantum mechanics. Developed in the first half of the twentieth century by a number of different physicists, quantum mechanics provides a radically different way of describing physical phenomena based on probability.
Charles-Augustin de Coulomb
Charles-Augustin de Coulomb (; ; 14 June 1736 – 23 August 1806) was a French military engineer and physicist. He is best known for developing what is now known as Coulomb's law, the description of the electrostatic force of attraction and repulsion, but also did important work on friction.
Castigliano's method
Castigliano's method, named for Carlo Alberto Castigliano, is a method for determining the displacements of a linear-elastic system based on the partial derivatives of the energy. He is known for his two theorems. The basic concept may be easy to understand by recalling that a change in energy is equal to the causing force times the resulting displacement. Therefore, the causing force is equal to the change in energy divided by the resulting displacement. Alternatively, the resulting displacement is equal to the change in energy divided by the causing force. Partial derivatives are needed to relate causing forces and resulting displacements to the change in energy. 
Castigliano's method for calculating forces is an application of his first theorem, which states:
In equation form,
where U is the strain energy.
First law of thermodynamics
That important state variable was first recognized and denoted formula_8 by Clausius in 1850, but he did not then name it, and he defined it in terms not only of work but also of heat transfer in the same process. It was also independently recognized in 1850 by Rankine, who also denoted it formula_8 ; and in 1851 by Kelvin who then called it "mechanical energy", and later "intrinsic energy". In 1865, after some hestitation, Clausius began calling his state function formula_8 "energy". In 1882 it was named as the "internal energy" by Helmholtz. If only adiabatic processes were of interest, and heat could be ignored, the concept of internal energy would hardly arise or be needed. The relevant physics would be largely covered by the concept of potential energy, as was intended in the 1847 paper of Helmholtz on the principle of conservation of energy, though that did not deal with forces that cannot be described by a potential, and thus did not fully justify the principle. Moreover, that paper was critical of the early work of Joule that had by then been performed. A great merit of the internal energy concept is that it frees thermodynamics from a restriction to cyclic processes, and allows a treatment in terms of thermodynamic states.
History of science
In 1687, Isaac Newton published the "Principia Mathematica", detailing two comprehensive and successful physical theories: Newton's laws of motion, which led to classical mechanics; and Newton's Law of Gravitation, which describes the fundamental force of gravity.
Anatoly Vlasov
Vlasov became world-famous for his work on plasma physics (1938) (see also ). He showed that the Boltzmann equation is not suitable for a description of plasma dynamics due to the existence of long range collective forces in the plasma. Instead, an equation known now as the Vlasov equation was suggested for the correct description to take into account the long range collective forces through a self-consistent field. The field is determined by taking moments of the distribution function described in Vlasov's equation to compute both the charge density and current density. Coupled with Maxwell's equations, the resulting system of differential equations are well-posed provided correct initial conditions and boundary conditions are provided.
History of centrifugal and centripetal forces
Later scientists pointed out (as did Newton) that the laws of mechanics were the same for all observers that differed only by uniform translation; that is, all observers that differed in motion only by a constant velocity. Hence, "absolute space" was not preferred, but only one of a set of frames related by Galilean transformations.
Ultimately this notion of the transformation properties of physical laws between frames played a more and more central role. 
It was noted that accelerating frames exhibited "fictitious forces" like the centrifugal force. These forces did not behave under transformation like other forces, providing a means of distinguishing them. This peculiarity of these forces led to the names "inertial forces", "pseudo-forces" or "fictitious forces". In particular, fictitious forces "did not appear at all" in some frames: those frames differing from that of the fixed stars by only a constant velocity. In short, a frame tied to the "fixed stars" is merely a member of the class of "inertial frames", and absolute space is an unnecessary and logically untenable concept. The preferred, or "inertial frames", were identifiable by the "absence of fictitious forces".
History of quantum mechanics
Building on pioneering work by Schwinger, Higgs and Goldstone, the physicists Glashow, Weinberg and Salam independently showed how the weak nuclear force and quantum electrodynamics could be merged into a single electroweak force, for which they received the 1979 Nobel Prize in Physics.
Faraday's law of induction
Michael Faraday explained electromagnetic induction using a concept he called lines of force. However, scientists at the time widely rejected his theoretical ideas, mainly because they were not formulated mathematically. An exception was James Clerk Maxwell, who in 1861–62 used Faraday's ideas as the basis of his quantitative electromagnetic theory. In Maxwell's papers, the time-varying aspect of electromagnetic induction is expressed as a differential equation which Oliver Heaviside referred to as Faraday's law even though it is different from the original version of Faraday's law, and does not describe motional EMF. Heaviside's version (see Maxwell–Faraday equation below) is the form recognized today in the group of equations known as Maxwell's equations.
Line of force
At first Faraday considered the physical reality of the "lines of force" as a possibility, yet several scholars agree that for Faraday their physical reality became a conviction. One scholar dates this change in the year 1838. Another scholar dates this final strengthening of his belief in 1852. Faraday experimentally studied lines of magnetic force and lines of electrostatic force, showing them not to fit action at a distance models. In 1852 Faraday wrote the paper "On the Physical Character of the Lines of Magnetic Force" which examined gravity, radiation, and electricity, and their possible relationships with the transmission medium, transmission propagation, and the receiving entity.
Two-body problem in general relativity
Nearly a century later, Isaac Newton had formulated his three laws of motion. In particular, Newton's second law states that a force "F" applied to a mass "m" produces an acceleration "a" given by the equation "F"="ma". Newton then posed the question: what must the force be that produces the elliptical orbits seen by Kepler? His answer came in his law of universal gravitation, which states that the force between a mass "M" and another mass "m" is given by the formula
Force
The fundamental theories for forces developed from the unification of different ideas. For example, Sir. Isaac Newton unified, with his universal theory of gravitation, the force responsible for objects falling near the surface of the Earth with the force responsible for the falling of celestial bodies about the Earth (the Moon) and around the Sun (the planets). Michael Faraday and James Clerk Maxwell demonstrated that electric and magnetic forces were unified through a theory of electromagnetism. In the 20th century, the development of quantum mechanics led to a modern understanding that the first three fundamental forces (all except gravity) are manifestations of matter (fermions) interacting by exchanging virtual particles called gauge bosons. This standard model of particle physics assumes a similarity between the forces and led scientists to predict the unification of the weak and electromagnetic forces in electroweak theory, which was subsequently confirmed by observation. The complete formulation of the standard model predicts an as yet unobserved Higgs mechanism, but observations such as neutrino oscillations suggest that the standard model is incomplete. A Grand Unified Theory that allows for the combination of the electroweak interaction with the strong force is held out as a possibility with candidate theories such as supersymmetry proposed to accommodate some of the outstanding unsolved problems in physics. Physicists are still attempting to develop self-consistent unification models that would combine all four fundamental interactions into a theory of everything. Einstein tried and failed at this endeavor, but currently the most popular approach to answering this question is string theory.
Optical force
The optical force is a phenomenon whereby beams of light can attract and repel each other. The force acts along an axis which is perpendicular to the light beams. Because of this, parallel beams can be induced to converge or diverge. The optical force works on a microscopic scale, and cannot currently be detected at larger scales. It was discovered by a team of Yale researchers led by electrical engineer Hong Tang.
Jordanus de Nemore
The medieval “science of weights” (i.e., mechanics) owes much of its importance to the work of Jordanus. In the "Elementa super demonstrationem ponderum", he introduces the concept of “positional gravity” and the use of component forces. Pierre Duhem (in his "Origines de la statique", 1905) thought that Jordanus also introduces infinitesimal considerations into statics in his discussion of "virtual" displacements (this being another interpretation of Duhem) of objects in equilibrium. He proves the law of the lever by means of the principle of work. The "De ratione ponderis" also proves the conditions of equilibrium of unequal weights on planes inclined at different angles – long before it was re-established by Simon Stevin (with his clootcrans -- "wreath of spheres" experiment) and later by Galileo.
Analogical models
The earliest such analogy is due to James Clerk Maxwell who, in 1873, associated mechanical force with electrical voltage. This analogy became so widespread that sources of voltage are still today referred to as electromotive force. The power conjugate of voltage is electric current which, in the Maxwell analogy, maps to mechanical velocity. Electrical impedance is the ratio of voltage and current, so by analogy, mechanical impedance is the ratio of force and velocity. The concept of impedance can be extended to other domains, for instance in acoustics and fluid flow it is the ratio of pressure to rate of flow. In general, impedance is the ratio of an "effort" variable and the "flow" variable that results. For this reason, the Maxwell analogy is often referred to as the impedance analogy, although the concept of impedance was not conceived until 1886 by Oliver Heaviside, some time after Maxwell's death.
History of physics
While it was recognized early in the 18th century that finding absolute theories of electrostatic and magnetic force akin to Newton's principles of motion would be an important achievement, none were forthcoming. This impossibility only slowly disappeared as experimental practice became more widespread and more refined in the early years of the 19th century in places such as the newly established Royal Institution in London. Meanwhile, the analytical methods of rational mechanics began to be applied to experimental phenomena, most influentially with the French mathematician Joseph Fourier's analytical treatment of the flow of heat, as published in 1822. Joseph Priestley proposed an electrical inverse-square law in 1767, and Charles-Augustin de Coulomb introduced the inverse-square law of electrostatics in 1798.
Coulomb's law
Early investigators of the 18th century who suspected that the electrical force diminished with distance as the force of gravity did (i.e., as the inverse square of the distance) included Daniel Bernoulli and Alessandro Volta, both of whom measured the force between plates of a capacitor, and Franz Aepinus who supposed the inverse-square law in 1758.
Equivalence principle
Dutch physicist and string theorist Erik Verlinde has generated a self-contained, logical derivation of the equivalence principle based on the starting assumption of a holographic universe. Given this situation, gravity would not be a true fundamental force as is currently thought but instead an "emergent property" related to entropy. Verlinde's entropic gravity theory apparently leads naturally to the correct observed strength of dark energy; previous failures to explain its incredibly small magnitude have been called by such people as cosmologist Michael Turner (who is credited as having coined the term "dark energy") as "the greatest embarrassment in the history of theoretical physics". However, it should be noted that these ideas are far from settled and still very controversial.
Electricity
Ørsted did not fully understand his discovery, but he observed the effect was reciprocal: a current exerts a force on a magnet, and a magnetic field exerts a force on a current. The phenomenon was further investigated by Ampère, who discovered that two parallel current-carrying wires exerted a force upon each other: two wires conducting currents in the same direction are attracted to each other, while wires containing currents in opposite directions are forced apart. The interaction is mediated by the magnetic field each current produces and forms the basis for the international definition of the ampere.
This relationship between magnetic fields and currents is extremely important, for it led to Michael Faraday's invention of the electric motor in 1821. Faraday's homopolar motor consisted of a permanent magnet sitting in a pool of mercury. A current was allowed through a wire suspended from a pivot above the magnet and dipped into the mercury. The magnet exerted a tangential force on the wire, making it circle around the magnet for as long as the current was maintained.
List of Dutch discoveries
In 1892, Hendrik Lorentz derived the modern form of the formula for the electromagnetic force which includes the contributions to the total force from both the electric and the magnetic fields. In many textbook treatments of classical electromagnetism, the Lorentz force law is used as the "definition" of the electric and magnetic fields E and B. To be specific, the Lorentz force is understood to be the following empirical statement:
Coulomb's law
Coulomb's law, or Coulomb's inverse-square law, is a law of physics for quantifying Coulomb's force, or electrostatic force. Electrostatic force is the amount of force with which stationary, electrically charged particles either repel, or attract each other. This force and the law for quantifying it, represent one of the most basic forms of force used in the physical sciences, and were an essential basis to the study and development of the theory and field of classical electromagnetism. The law was first published in 1785 by French physicist Charles-Augustin de Coulomb.
Potentiality and actuality
There was an adaptation of at least one aspect of Aristotle's potentiality and actuality distinction, which has become part of modern physics, although as per Bacon's approach it is a generalized form of energy, not one connected to specific forms for specific things. The definition of energy in modern physics as the product of mass and the square of velocity, was derived by Leibniz, as a correction of Descartes, based upon Galileo's investigation of falling bodies. He preferred to refer to it as an "entelecheia" or "living force" (Latin "vis viva"), but what he defined is today called "kinetic energy", and was seen by Leibniz as a modification of Aristotle's "energeia", and his concept of the potential for movement which is in things. Instead of each type of physical thing having its own specific tendency to a way of moving or changing, as in Aristotle, Leibniz said that instead, force, power, or motion itself could be transferred between things of different types, in such a way that there is a general conservation of this energy. In other words, Leibniz's modern version of entelechy or energy obeys its own laws of nature, whereas different types of things do not have their own separate laws of nature. Leibniz wrote: ...the entelechy of Aristotle, which has made so much noise, is nothing else but force or activity ; that is, a state from which action naturally flows if nothing hinders it. But matter, primary and pure, taken without the souls or lives which are united to it, is purely passive ; properly speaking also it is not a substance, but something incomplete.
Equations of motion
Galileo was the first to show that the path of a projectile is a parabola. Galileo had an understanding of centrifugal force and gave a correct definition of momentum. This emphasis of momentum as a fundamental quantity in dynamics is of prime importance. He measured momentum by the product of velocity and weight; mass is a later concept, developed by Huygens and Newton. In the swinging of a simple pendulum, Galileo says in "Discourses" that "every momentum acquired in the descent along an arc is equal to that which causes the same moving body to ascend through the same arc." His analysis on projectiles indicates that Galileo had grasped the first law and the second law of motion. He did not generalize and make them applicable to bodies not subject to the earth's gravitation. That step was Newton's contribution.
Albert Einstein
Albert Einstein (; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist who developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics). His work is also known for its influence on the philosophy of science. He is best known to the general public for his mass–energy equivalence formula , which has been dubbed "the world's most famous equation". He received the 1921 Nobel Prize in Physics "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect", a pivotal step in the development of quantum theory.
Force
A static equilibrium between two forces is the most usual way of measuring forces, using simple devices such as weighing scales and spring balances. For example, an object suspended on a vertical spring scale experiences the force of gravity acting on the object balanced by a force applied by the "spring reaction force", which equals the object's weight. Using such tools, some quantitative force laws were discovered: that the force of gravity is proportional to volume for objects of constant density (widely exploited for millennia to define standard weights); Archimedes' principle for buoyancy; Archimedes' analysis of the lever; Boyle's law for gas pressure; and Hooke's law for springs. These were all formulated and experimentally verified before Isaac Newton expounded his Three Laws of Motion.
Gaspard-Gustave de Coriolis
Gaspard-Gustave de Coriolis (; 21 May 1792 – 19 September 1843) was a French mathematician, mechanical engineer and scientist. He is best known for his work on the supplementary forces that are detected in a rotating frame of reference, leading to the Coriolis effect. He was the first to use the term "work" for the transfer of energy by a force acting through a distance.
Trouton–Noble experiment
A solution without compensating forces or redefinitions of force and equilibrium was published by Richard C. Tolman and Paul Sophus Epstein in 1911. A similar solution was re-discovered by Franklin (2006).
They alluded to the fact that force and acceleration do not always have the same direction, that is, the relation of mass, force and acceleration has tensor character in relativity. So the role played by the concept of force in relativity is very different from that of Newtonian mechanics.
Nuclear force
Throughout the 1930s a group at Columbia University led by I. I. Rabi developed magnetic resonance techniques to determine the magnetic moments of nuclei. These measurements led to the discovery in 1939 that the deuteron also possessed an electric quadrupole moment. This electrical property of the deuteron had been interfering with the measurements by the Rabi group. The deuteron, composed of a proton and a neutron, is one of the simplest nuclear systems. The discovery meant that the physical shape of the deuteron was not symmetric, which provided valuable insight into the nature of the nuclear force binding nucleons. In particular, the result showed that the nuclear force was not a central force, but had a tensor character. Hans Bethe identified the discovery of the deuteron's quadrupole moment as one of the important events during the formative years of nuclear physics.
History of physics
The move towards a rational understanding of nature began at least since the Archaic period in Greece (650–480 BCE) with the Pre-Socratic philosophers. The philosopher Thales of Miletus (7th and 6th centuries BCE), dubbed "the Father of Science" for refusing to accept various supernatural, religious or mythological explanations for natural phenomena, proclaimed that every event had a natural cause. Thales also made advancements in 580 BCE by suggesting that water is the basic element, experimenting with the attraction between magnets and rubbed amber and formulating the first recorded cosmologies. Anaximander, famous for his proto-evolutionary theory, disputed the Thales' ideas and proposed that rather than water, a substance called "apeiron" was the building block of all matter. Around 500 BCE, Heraclitus proposed that the only basic law governing the Universe was the principle of change and that nothing remains in the same state indefinitely. This observation made him one of the first scholars in ancient physics to address the role of time in the universe, a key and sometimes contentious concept in modern and present-day physics. The early physicist Leucippus (fl. first half of the 5th century BCE) adamantly opposed the idea of direct divine intervention in the universe, proposing instead that natural phenomena had a natural cause. Leucippus and his student Democritus were the first to develop the theory of atomism, the idea that everything is composed entirely of various imperishable, indivisible elements called atoms.
Dynamics (mechanics)
Dynamics is the branch of classical mechanics concerned with the study of forces and their effects on motion. Isaac Newton defined the fundamental physical laws which govern dynamics in physics, especially his second law of motion.
Force dynamics
Introduced by cognitive linguist Leonard Talmy in 1981, force dynamics started out as a generalization of the traditional notion of the causative, dividing "causation" into finer primitives and considering the notions of "letting", "hindering", and "helping". Talmy further developed the field in his 1985, 1988 and 2000 works.
Moment (physics)
The concept of moment in physics is derived from the mathematical concept of moments. The principle of moments is derived from Archimedes' discovery of the operating principle of the lever. In the lever one applies a force, in his day most often human muscle, to an arm, a beam of some sort. Archimedes noted that the amount of force applied to the object, the moment of force, is defined as M = rF, where F is the applied force, and r is the distance from the applied force to object. However, historical evolution of the term 'moment' and its use in different branches of science, such as mathematics, physics and engineering, is unclear.
History of centrifugal and centripetal forces
Christiaan Huygens coined the term "centrifugal force" in his 1659 "De Vi Centrifuga" and wrote of it in his 1673 "Horologium Oscillatorium" on pendulums. Isaac Newton coined the term "centripetal force" ("vis centripita") in his discussions of gravity in his 1684 "De Motu Corporum".
Force
Since forces are perceived as pushes or pulls, this can provide an intuitive understanding for describing forces. As with other physical concepts (e.g. temperature), the intuitive understanding of forces is quantified using precise operational definitions that are consistent with direct observations and compared to a standard measurement scale. Through experimentation, it is determined that laboratory measurements of forces are fully consistent with the conceptual definition of force offered by Newtonian mechanics.
Outline of Albert Einstein
Albert Einstein – deceased German-born theoretical physicist. He developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics). Einstein's work is also known for its influence on the philosophy of science. Einstein is best known by the general public for his mass–energy equivalence formula (which has been dubbed "the world's most famous equation"). He received the 1921 Nobel Prize in Physics "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect", a pivotal step in the evolution of quantum theory. Einstein published more than 300 scientific papers along with over 150 non-scientific works. Einstein's intellectual achievements and originality have made the word "Einstein" synonymous with "genius".
Einstein family
Scientific publications by Albert Einstein
Cavendish experiment
The Cavendish experiment, performed in 1797–1798 by British scientist Henry Cavendish, was the first experiment to measure the force of gravity between masses in the laboratory and the first to yield accurate values for the gravitational constant. Because of the unit conventions then in use, the gravitational constant does not appear explicitly in Cavendish's work. Instead, the result was originally expressed as the specific gravity of the Earth, or equivalently the mass of the Earth. His experiment gave the first accurate values for these geophysical constants.
History of electromagnetic theory
Italian physician Gerolamo Cardano wrote about electricity in "De Subtilitate" (1550) distinguishing, perhaps for the first time, between electrical and magnetic forces.
Deductive-nomological model
In 1925, Werner Heisenberg as well as Erwin Schrödinger independently formalized quantum mechanics (QM). Despite clashing explanations, the two theories made identical predictions. Paul Dirac's 1928 model of the electron was set to special relativity, launching QM into the first quantum field theory (QFT), quantum electrodynamics (QED). From it, Dirac interpreted and predicted the electron's antiparticle, soon discovered and termed "positron", but the QED failed electrodynamics at high energies. Elsewhere and otherwise, strong nuclear force and weak nuclear force were discovered.
Electricity
Ørsted's discovery in 1821 that a magnetic field existed around all sides of a wire carrying an electric current indicated that there was a direct relationship between electricity and magnetism. Moreover, the interaction seemed different from gravitational and electrostatic forces, the two forces of nature then known. The force on the compass needle did not direct it to or away from the current-carrying wire, but acted at right angles to it. Ørsted's slightly obscure words were that "the electric conflict acts in a revolving manner." The force also depended on the direction of the current, for if the flow was reversed, then the force did too.
Biefeld–Brown effect
The "Biefeld–Brown effect" was the name given to a phenomenon observed by Thomas Townsend Brown while he was experimenting with X-ray tubes during the 1920s while he was still in high school. When he applied a high voltage electrical charge to a Coolidge tube that he placed on a scale, Brown noticed a difference in the tubes mass depending on orientation, implying some kind of net force. This discovery caused him to assume that he had somehow influenced gravity electronically and led him to design a propulsion system based on this phenomenon. On 15 April 1927, he applied for a patent, entitled "Method of Producing Force or Motion," that described his invention as an electrical-based method that could control gravity to produce linear force or motion. In 1929, Brown published an article for the popular American magazine "Science and Invention", which detailed his work. The article also mentioned the "gravitator," an invention by Brown which produced motion without the use of electromagnetism, gears, propellers, or wheels, but instead using the principles of what he called "electro-gravitation." He also claimed that the asymmetric capacitors were capable of generating mysterious fields that interacted with the Earth's gravitational pull and envisioned a future where gravitators would propel ocean liners and even space cars. At some point this effect also gained the moniker "Biefeld–Brown effect", probably coined by Brown to claim Denison University professor of physics and astronomy Paul Alfred Biefeld as his mentor and co-experimenter. Brown attended Denison for a year before he dropped out and records of him even having an association with Biefeld are sketchy at best.
Theory of everything
Gravity and electromagnetism could always peacefully coexist as entries in a list of classical forces, but for many years it seemed that gravity could not even be incorporated into the quantum framework, let alone unified with the other fundamental forces. For this reason, work on unification, for much of the twentieth century, focused on understanding the three "quantum" forces: electromagnetism and the weak and strong forces. The first two were combined in 1967–68 by Sheldon Glashow, Steven Weinberg, and Abdus Salam into the "electroweak" force.
Electroweak unification is a broken symmetry: the electromagnetic and weak forces appear distinct at low energies because the particles carrying the weak force, the W and Z bosons, have non-zero masses of and , whereas the photon, which carries the electromagnetic force, is massless. At higher energies Ws and Zs can be created easily and the unified nature of the force becomes apparent.
Experimental physics
Experimental physics is considered to have reached a high point with the publication of the "Philosophiae Naturalis Principia Mathematica" in 1687 by Sir Isaac Newton (1643–1727). In 1687, Newton published the "Principia", detailing two comprehensive and successful physical theories: Newton's laws of motion, from which arise classical mechanics; and Newton's law of universal gravitation, which describes the fundamental force of gravity. Both theories agreed well with experiment. The "Principia" also included several theories in fluid dynamics.
Ernst Stueckelberg
Ernst Carl Gerlach Stueckelberg (baptised as Johann Melchior Ernst Karl Gerlach Stückelberg, full name after 1911: Baron Ernst Carl Gerlach Stueckelberg von Breidenbach zu Breidenstein und Melsbach; 1 February 1905 – 4 September 1984) was a Swiss mathematician and physicist, regarded as one of the most eminent physicists of the 20th century. Despite making key advances in theoretical physics, including the exchange particle model of fundamental forces, causal S-matrix theory, and the renormalization group, his idiosyncratic style and publication in minor journals led to his work being unrecognized until the mid-1990s.
History of energy
Émilie marquise du Châtelet in her book Institutions de Physique ("Lessons in Physics"), published in 1740, incorporated the idea of Leibniz with practical observations of Gravesande to show that the "quantity of motion" of a moving object is proportional to its mass and its velocity squared (not the velocity itself as Newton taught—what was later called momentum).
Line of force
Lines of force originated with Michael Faraday, whose theory holds that all of reality is made up of force "itself". His theory predicts that electricity, light, and gravity have finite propagation delays. The theories and experimental data of later scientific figures such as Maxwell, Hertz, Einstein, and others are in agreement with the ramifications of Faraday's theory. Nevertheless, Faraday's theory remains distinct. Unlike Faraday, Maxwell and others (e.g., J.J. Thomson) thought that light and electricity must propagate through an ether. In Einstein's relativity, there is no ether, yet the physical reality of force is much weaker than in the theories of Faraday.
List of Dutch discoveries
Christiaan Huygens stated what is now known as the second of Newton's laws of motion in a quadratic form. In 1659 he derived the now standard formula for the centripetal force, exerted by an object describing a circular motion, for instance on the string to which it is attached. In modern notation:
A Treatise on Electricity and Magnetism
Hermann von Helmholtz (1881): "Now that the mathematical interpretations of Faraday's conceptions regarding the nature of electric and magnetic force has been given by Clerk Maxwell, we see how great a degree of exactness and precision was really hidden behind Faraday's words…it is astonishing in the highest to see what a large number of general theories, the mechanical deduction of which requires the highest powers of mathematical analysis, he has found by a kind of intuition, with the security of instinct, without the help of a single mathematical formula."
Classical central-force problem
The term "r" occurs in all the force laws above, indicating that the addition of the inverse-cube force does not influence the solubility of the problem in terms of known functions. Newton showed that, with adjustments in the initial conditions, the addition of such a force does not affect the radial motion of the particle, but multiplies its angular motion by a constant factor "k". An extension of Newton's theorem was discovered in 2000 by Mahomed and Vawda.
Nuclear physics
The study of the strong and weak nuclear forces (the latter explained by Enrico Fermi via Fermi's interaction in 1934) led physicists to collide nuclei and electrons at ever higher energies. This research became the science of particle physics, the crown jewel of which is the standard model of particle physics which describes the strong, weak, and electromagnetic forces.
Coriolis force
Gaspard-Gustave Coriolis published a paper in 1835 on the energy yield of machines with rotating parts, such as waterwheels. That paper considered the supplementary forces that are detected in a rotating frame of reference. Coriolis divided these supplementary forces into two categories. The second category contained a force that arises from the cross product of the angular velocity of a coordinate system and the projection of a particle's velocity into a plane perpendicular to the system's axis of rotation. Coriolis referred to this force as the "compound centrifugal force" due to its analogies with the centrifugal force already considered in category one. The effect was known in the early 20th century as the "acceleration of Coriolis", and by 1920 as "Coriolis force".
Lorentz force
The modern concept of electric and magnetic fields first arose in the theories of Michael Faraday, particularly his idea of lines of force, later to be given full mathematical description by Lord Kelvin and James Clerk Maxwell. From a modern perspective it is possible to identify in Maxwell's 1865 formulation of his field equations a form of the Lorentz force equation in relation to electric currents, however, in the time of Maxwell it was not evident how his equations related to the forces on moving charged objects. J. J. Thomson was the first to attempt to derive from Maxwell's field equations the electromagnetic forces on a moving charged object in terms of the object's properties and external fields. Interested in determining the electromagnetic behavior of the charged particles in cathode rays, Thomson published a paper in 1881 wherein he gave the force on the particles due to an external magnetic field as
Thomson derived the correct basic form of the formula, but, because of some miscalculations and an incomplete description of the displacement current, included an incorrect scale-factor of a half in front of the formula. Oliver Heaviside invented the modern vector notation and applied it to Maxwell's field equations; he also (in 1885 and 1889) had fixed the mistakes of Thomson's derivation and arrived at the correct form of the magnetic force on a moving charged object. Finally, in 1895, Hendrik Lorentz derived the modern form of the formula for the electromagnetic force which includes the contributions to the total force from both the electric and the magnetic fields. Lorentz began by abandoning the Maxwellian descriptions of the ether and conduction. Instead, Lorentz made a distinction between matter and the luminiferous aether and sought to apply the Maxwell equations at a microscopic scale. Using Heaviside's version of the Maxwell equations for a stationary ether and applying Lagrangian mechanics (see below), Lorentz arrived at the correct and complete form of the force law that now bears his name.
Newton's theorem of revolving orbits
Isaac Newton derived this theorem in Propositions 43–45 of Book I of his "Philosophiæ Naturalis Principia Mathematica", first published in 1687. In Proposition 43, he showed that the added force must be a central force, one whose magnitude depends only upon the distance "r" between the particle and a point fixed in space (the center). In Proposition 44, he derived a formula for the force, showing that it was an inverse-cube force, one that varies as the inverse cube of "r". In Proposition 45 Newton extended his theorem to arbitrary central forces by assuming that the particle moved in nearly circular orbit.
George Miller Beard
He described the force as "somewhere between light and heat on the one hand and magnetism and electricity on the other, with some features of all these forces."
Water wheel
Millwrights distinguished between the two forces, impulse and weight, at work in water wheels long before 18th-century Europe. Fitzherbert, a 16th-century agricultural writer, wrote "druieth the wheel as well as with the weight of the water as with strengthe [impulse]". Leonardo da Vinci also discussed water power, noting "the blow [of the water] is not weight, but excites a power of weight, almost equal to its own power". However, even realisation of the two forces, weight and impulse, confusion remained over the advantages and disadvantages of the two, and there was no clear understanding of the superior efficiency of weight. Prior to 1750 it was unsure as to which force was dominant and was widely understood that both forces were operating with equal inspiration amongst one another. The waterwheel, sparked questions of the laws of nature, specifically the laws of force. Evangelista Torricelli's work on water wheels used an analysis of Galileo's work on falling bodies, that the velocity of a water sprouting from an orifice under its head was exactly equivalent to the velocity a drop of water acquired in falling freely from the same height.
Le Sage's theory of gravitation
Already in 1690 Fatio assumed, that the "push force" exerted by the particles on a plain surface is the sixth part of the force, which would be produced if all particles are lined up normal to the surface. Fatio now gave a proof of this proposal by determination of the force, which is exerted by the particles on a certain point zz. He derived the formula "p=ρvzz/6". This solution is very similar to the formula known in the kinetic theory of gases "p=ρv/3", which was found by Daniel Bernoulli in 1738. This was the first time that a solution analogous to the similar result in kinetic theory was pointed out - long "before" the basic concept of the latter theory was developed. However, Bernoulli's value is twice as large as Fatio's one, because according to Zehe, Fatio only calculated the value "mv" for the change of impulse after the collision, but not "2mv" and therefore got the wrong result. (His result is only correct in the case of totally inelastic collisions.) Fatio tried to use his solution not only for explaining gravitation, but for explaining the behaviour of gases as well. He tried to construct a thermometer, which should indicate the "state of motion" of the air molecules and therefore estimate the temperature. But Fatio (unlike Bernoulli) did not "identify" heat and the movements of the air particles - he used another fluid, which should be responsible for this effect. It is also unknown, whether Bernoulli was influenced by Fatio or not.
Dynamics (mechanics)
Newton described force as the ability to cause a mass to accelerate. His three laws can be summarized as follows:
Biomechanics
The next major bio-mechanic, Giovanni Alfonso Borelli, was the first to understand that “the levers of the musculature system magnify motion rather than force, so that muscles must produce much larger forces than those resisting the motion”. Using the works of Galileo and building off from them, Borelli figured out the forces required for equilibrium in various joints of the human body. He even discovered the human center of gravity and air volume as well as  muscle elasticity. His work is often considered the most important in the history of bio-mechanics because he made so many new discoveries that opened the way for the future generations to continue his work and studies.
Physicist
The study and practice of physics is based on an intellectual ladder of discoveries and insights from ancient times to the present. Many mathematical and physical ideas used today found their earliest expression in ancient Greek culture, for example in the work of Euclid, Thales of Miletus, Archimedes and Aristarchus. Roots also emerged in ancient Asian culture and in the Islamic medieval period, for example the work of Alhazen in the 11th century. The modern scientific worldview and the bulk of physics education can be said to flow from the scientific revolution in Europe, starting with the work of Galileo Galilei and Johannes Kepler in the early 1600s. Newton's laws of motion and Newton's law of universal gravitation were formulated in the 17th century. The experimental discoveries of Faraday and the theory of Maxwell's equations of electromagnetism were developmental high points during the 19th century. Many physicists contributed to the development of quantum mechanics in the early-to-mid 20th century. New knowledge in the early 21st century includes a large increase in understanding physical cosmology.
Force
The origin of electric and magnetic fields would not be fully explained until 1864 when James Clerk Maxwell unified a number of earlier theories into a set of 20 scalar equations, which were later reformulated into 4 vector equations by Oliver Heaviside and Josiah Willard Gibbs. These "Maxwell Equations" fully described the sources of the fields as being stationary and moving charges, and the interactions of the fields themselves. This led Maxwell to discover that electric and magnetic fields could be "self-generating" through a wave that traveled at a speed that he calculated to be the speed of light. This insight united the nascent fields of electromagnetic theory with optics and led directly to a complete description of the electromagnetic spectrum.
List of medieval European scientists
Avempace (died 1138), a famous physicist from Muslim Spain who had an important influence on later physicists such as Galileo. He was the first to theorize the concept of a reaction force for every force exerted.
History of physics
In 1714, Brook Taylor derived the fundamental frequency of a stretched vibrating string in terms of its tension and mass per unit length by solving a differential equation. The Swiss mathematician Daniel Bernoulli (1700–1782) made important mathematical studies of the behavior of gases, anticipating the kinetic theory of gases developed more than a century later, and has been referred to as the first mathematical physicist. In 1733, Daniel Bernoulli derived the fundamental frequency and harmonics of a hanging chain by solving a differential equation. In 1734, Bernoulli solved the differential equation for the vibrations of an elastic bar clamped at one end. Bernoulli's treatment of fluid dynamics and his examination of fluid flow was introduced in his 1738 work "Hydrodynamica".
Force
The electrostatic force was first described in 1784 by Coulomb as a force that existed intrinsically between two charges. The properties of the electrostatic force were that it varied as an inverse square law directed in the radial direction, was both attractive and repulsive (there was intrinsic polarity), was independent of the mass of the charged objects, and followed the superposition principle. Coulomb's law unifies all these observations into one succinct statement.
Johannes Stark
Johannes Stark (, 15 April 1874 – 21 June 1957) was a German physicist and Physics Nobel Prize laureate. He is known for identifying the Stark effect. He was later closely involved with the "Deutsche Physik" movement under the Nazi regime.
History of physics
In 1905 a young, 26-year-old German physicist (then a Bern patent clerk) named Albert Einstein (1879–1955), showed how measurements of time and space are affected by motion between an observer and what is being observed. To say that Einstein's radical theory of relativity revolutionized science is no exaggeration. Although Einstein made many other important contributions to science, the theory of relativity alone represents one of the greatest intellectual achievements of all time. Although the concept of relativity was not introduced by Einstein, his major contribution was the recognition that the speed of light in a vacuum is constant, i.e. the same for all observers, and an absolute physical boundary for motion. This does not impact a person's day-to-day life since most objects travel at speeds much slower than light speed. For objects travelling near light speed, however, the theory of relativity shows that clocks associated with those objects will run more slowly and that the objects shorten in length according to measurements of an observer on Earth. Einstein also derived the famous equation, "E" = "mc", which expresses the equivalence of mass and energy.
Force
The notion "force" keeps its meaning in quantum mechanics, though one is now dealing with operators instead of classical variables and though the physics is now described by the Schrödinger equation instead of Newtonian equations. This has the consequence that the results of a measurement are now sometimes "quantized", i.e. they appear in discrete portions. This is, of course, difficult to imagine in the context of "forces". However, the potentials "V"("x","y","z") or fields, from which the forces generally can be derived, are treated similarly to classical position variables, i.e., formula_36.
Experimental physics
As a distinct field, experimental physics was established in early modern Europe, during what is known as the Scientific Revolution, by physicists such as Galileo Galilei, Christiaan Huygens, Johannes Kepler, Blaise Pascal and Sir Isaac Newton. In the early 17th century, Galileo made extensive use of experimentation to validate physical theories, which is the key idea in the modern scientific method. Galileo formulated and successfully tested several results in dynamics, in particular the law of inertia, which later became the first law in Newton's laws of motion. In Galileo's "Two New Sciences", a dialogue between the characters Simplicio and Salviati discuss the motion of a ship (as a moving frame) and how that ship's cargo is indifferent to its motion. Huygens used the motion of a boat along a Dutch canal to illustrate an early form of the conservation of momentum.
Exchange force
One of the earliest uses of the term "interaction" was in a discussion by Niels Bohr in 1913 of the interaction between the negative electron and the positive nucleus. Exchange forces were introduced by Werner Heisenberg (1932) and Ettore Majorana (1933) in order to account for the saturation of binding energy and of nuclear density. This was done in analogy to the quantum mechanical theory of covalent bonds, such as exist between two hydrogen atoms in the hydrogen molecule wherein the chemical force is attractive if the wave function is symmetric under exchange of coordinates of the electrons and is repulsive if the wave function is anti-symmetric in this respect.
History of the philosophy of field theory
Field theory, the study of dynamical fields in physics, was originally a mathematical formulation of Newtonian mechanics. The success of Newtonian physics since the publication of Isaac Newton's "Principia" in 1687 provided a framework with which to investigate the motion and forces associated with electricity and magnetism. Charles-Augustin de Coulomb showed in 1785 that the repulsive force between two electrically charged spheres obeys the same (up to a sign) force law as Newton's law of universal gravitation: the force between two bodies is directed along the line separating the bodies and its magnitude is proportional to the product of their charges (for gravitation, their masses) divided by the square of their distance apart. André-Marie Ampère showed in 1823 that the force between infinitesimal lengths of current-carrying wires similarly obeys an inverse-square law such that the force is directed along the line of separation between the wire elements.
Force
where
Force
Subsequent mathematicians and physicists found the construct of the "electric field" to be useful for determining the electrostatic force on an electric charge at any point in space. The electric field was based on using a hypothetical "test charge" anywhere in space and then using Coulomb's Law to determine the electrostatic force. Thus the electric field anywhere in space is defined as
Inertia
Nevertheless, despite defining the concept so elegantly in his laws of motion, even Newton did not actually use the term "inertia" to refer to his First Law. In fact, Newton originally viewed the phenomenon he described in his First Law of Motion as being caused by "innate forces" inherent in matter, which resisted any acceleration. Given this perspective, and borrowing from Kepler, Newton attributed the term "inertia" to mean "the innate force possessed by an object which resists changes in motion"; thus, Newton defined "inertia" to mean the cause of the phenomenon, rather than the phenomenon itself. However, Newton's original ideas of "innate resistive force" were ultimately problematic for a variety of reasons, and thus most physicists no longer think in these terms. As no alternate mechanism has been readily accepted, and it is now generally accepted that there may not be one which we can know, the term "inertia" has come to mean simply the phenomenon itself, rather than any inherent mechanism. Thus, ultimately, "inertia" in modern classical physics has come to be a name for the same phenomenon described by Newton's First Law of Motion, and the two concepts are now considered to be equivalent.
Potential energy
The term "potential energy" was introduced by the 19th-century Scottish engineer and physicist William Rankine, although it has links to Greek philosopher Aristotle's concept of potentiality.
Potential energy is associated with forces that act on a body in a way that the total work done by these forces on the body depends only on the initial and final positions of the body in space. These forces, that are called "conservative forces", can be represented at every point in space by vectors expressed as gradients of a certain scalar function called "potential".
Experimental physics
Besides classical mechanics and thermodynamics, another great field of experimental inquiry within physics was the nature of electricity. Observations in the 17th and eighteenth century by scientists such as Robert Boyle, Stephen Gray, and Benjamin Franklin created a foundation for later work. These observations also established our basic understanding of electrical charge and current. By 1808 John Dalton had discovered that atoms of different elements have different weights and proposed the modern theory of the atom.
Force
Aristotelian physics began facing criticism in medieval science, first by John Philoponus in the 6th century.
Kinetic energy
The principle in classical mechanics that "E ∝ mv" was first developed by Gottfried Leibniz and Johann Bernoulli, who described kinetic energy as the "living force", "vis viva". Willem 's Gravesande of the Netherlands provided experimental evidence of this relationship. By dropping weights from different heights into a block of clay, Willem 's Gravesande determined that their penetration depth was proportional to the square of their impact speed. Émilie du Châtelet recognized the implications of the experiment and published an explanation.
Lorentz force
Early attempts to quantitatively describe the electromagnetic force were made in the mid-18th century. It was proposed that the force on magnetic poles, by Johann Tobias Mayer and others in 1760, and electrically charged objects, by Henry Cavendish in 1762, obeyed an inverse-square law. However, in both cases the experimental proof was neither complete nor conclusive. It was not until 1784 when Charles-Augustin de Coulomb, using a torsion balance, was able to definitively show through experiment that this was true. Soon after the discovery in 1820 by H. C. Ørsted that a magnetic needle is acted on by a voltaic current, André-Marie Ampère that same year was able to devise through experimentation the formula for the angular dependence of the force between two current elements. In all these descriptions, the force was always given in terms of the properties of the objects involved and the distances between them rather than in terms of electric and magnetic fields.
Unified field theory
The first successful classical unified field theory was developed by James Clerk Maxwell. In 1820 Hans Christian Ørsted discovered that electric currents exerted forces on magnets, while in 1831, Michael Faraday made the observation that time-varying magnetic fields could induce electric currents. Until then, electricity and magnetism had been thought of as unrelated phenomena. In 1864, Maxwell published his famous paper on a dynamical theory of the electromagnetic field. This was the first example of a theory that was able to encompass previously separate field theories (namely electricity and magnetism) to provide a unifying theory of electromagnetism. By 1905, Albert Einstein had used the constancy of the speed of light in Maxwell's theory to unify our notions of space and time into an entity we now call spacetime and in 1915 he expanded this theory of special relativity to a description of gravity, general relativity, using a field to describe the curving geometry of four-dimensional spacetime.
Abdus Salam
During his visit at the Institute of Physics of Quaid-i-Azam University in 1979, Salam had explained after receiving his award: "Physicists believed there are four fundamental forces of nature; the gravitational force, the weak and strong nuclear force, and the electromagnetic force". Salam was a firm believer that "scientific thought is the common heritage of mankind", and that developing nations needed to help themselves and invest in their own scientists to boost development and reduce the gap between the Global South and the Global North, thus contributing to a more peaceful world.
Women in science
Émilie du Châtelet, a close friend of Voltaire, was the first scientist to appreciate the significance of kinetic energy, as opposed to momentum. She repeated and described the importance of an experiment originally devised by Willem 's Gravesande showing the impact of falling objects is proportional not to their velocity, but to the velocity squared. This understanding is considered to have made a profound contribution to Newtonian mechanics. In 1749 she completed the French translation of Newton's "Philosophiae Naturalis Principia Mathematica" (the "Principia"), including her derivation of the notion of conservation of energy from its principles of mechanics. Published ten years after her death, her translation and commentary of the "Principia" contributed to the completion of the scientific revolution in France and to its acceptance in Europe.
Froude–Krylov force
In fluid dynamics, the Froude–Krylov force—sometimes also called the Froude–Kriloff force—is a hydrodynamical force named after William Froude and Alexei Krylov. The Froude–Krylov force is the force introduced by the unsteady pressure field generated by "undisturbed" waves. The Froude–Krylov force does, together with the diffraction force, make up the total non-viscous forces acting on a floating body in regular waves. The diffraction force is due to the floating body disturbing the waves.
John Ernst Worrell Keely
Burk and Scott reported their findings to Mrs Moore, who was concerned by the negative report, and also by dismissive articles in the press. It was reported on March 22, 1896 that Mrs Bloomfield Moore had arranged with Professor Wentworth Lascelles Scott of London to investigate Keely's claims of etheric force and also to examine his other inventions. It was said that "an important series of tests will be made in the presence of the scientist". Lascelles Scott was allowed to examine whatever he wanted and had complete instructions on its use from Keely. After spending a month investigating, Lascelles Scott stated to a meeting of the Franklin Institute that "Keely has demonstrated to me, in a way which is absolutely unquestionable, the existence of a force hitherto unknown."
History of centrifugal and centripetal forces
Newton himself appears to have previously supported an approach similar to that of Leibniz. Later, Newton in his "Principia" crucially limited the description of the dynamics of planetary motion to a frame of reference in which the point of attraction is fixed. In this description, Leibniz's centrifugal force was not needed and was replaced by only continually inward forces toward the fixed point. Newton objected to Leibniz's equation on the grounds that it allowed for the centrifugal force to have a different value from the centripetal force, arguing on the basis of his third law of motion, that the centrifugal force and the centripetal force must constitute an equal and opposite action-reaction pair. In this however, Newton was mistaken, as the reactive centrifugal force which is required by the third law of motion is a completely separate concept from the centrifugal force of Leibniz's equation.
Hermann von Helmholtz
Drawing on the earlier work of Sadi Carnot, Benoît Paul Émile Clapeyron and James Prescott Joule, he postulated a relationship between mechanics, heat, light, electricity and magnetism by treating them all as manifestations of a single "force" (energy in modern terms), though 3 years after a similar postulation by William Robert Grove . He published his theories in his book "Über die Erhaltung der Kraft" ("On the Conservation of Force", 1847).
Quantum gravity
The current understanding of gravity is based on Albert Einstein's general theory of relativity, which is formulated within the framework of classical physics. On the other hand, the other three fundamental forces of physics are described within the framework of quantum mechanics and quantum field theory, radically different formalisms for describing physical phenomena. It is sometimes argued that a quantum mechanical description of gravity is necessary on the grounds that one cannot consistently couple a classical system to a quantum one.
Force
Since antiquity the concept of force has been recognized as integral to the functioning of each of the simple machines. The mechanical advantage given by a simple machine allowed for less force to be used in exchange for that force acting over a greater distance for the same amount of work. Analysis of the characteristics of forces ultimately culminated in the work of Archimedes who was especially famous for formulating a treatment of buoyant forces inherent in fluids.
Force
The use of Newton's Second Law as a "definition" of force has been disparaged in some of the more rigorous textbooks, because it is essentially a mathematical truism. Notable physicists, philosophers and mathematicians who have sought a more explicit definition of the concept of force include Ernst Mach and Walter Noll.
Force Concept Inventory
The Force Concept Inventory is a test measuring mastery of concepts commonly taught in a first semester of physics developed by Hestenes, Halloun, Wells, and Swackhamer (1985). It was the first such "concept inventory" and several others have been developed since for a variety of topics. The FCI was designed to assess student understanding of the Newtonian concepts of force. Hestenes (1998) found that while "nearly 80% of the [students completing introductory college physics courses] could state Newton's Third Law at the beginning of the course. FCI data showed that less than 15% of them fully understood it at the end". These results have been replicated in a number of studies involving students at a range of institutions (see sources section below), and have led to greater recognition in the physics education research community of the importance of students' "active engagement" with the materials to be mastered.
History of centrifugal and centripetal forces
It wasn't until the latter half of the 18th century that the modern "fictitious force" understanding of the centrifugal force as a pseudo-force artifact of rotating reference frames took shape. In a 1746 memoir by Daniel Bernoulli, "the idea that the centrifugal force is fictitious emerges unmistakably." Bernoulli, in seeking to describe the motion of an object relative to an arbitrary point, showed that the magnitude of the centrifugal force depended on which arbitrary point was chosen to measure circular motion about. Later in the 18th century Joseph Louis Lagrange in his "Mécanique Analytique" explicitly stated that the centrifugal force depends on the rotation of a system of perpendicular axes. 
In 1835, Gaspard-Gustave Coriolis analyzed arbitrary motion in rotating systems, specifically in relation to waterwheels. He coined the phrase "compound centrifugal force" for a term which bore a similar mathematical expression to that of centrifugal force, albeit that it was multiplied by a factor of two. 
The force in question was perpendicular to both the velocity of an object relative to a rotating frame of reference and the axis of rotation of the frame. Compound centrifugal force eventually came to be known as the Coriolis Force.
Ampère's force law
Following Ampère, a number of scientists, including Wilhelm Weber, Rudolf Clausius, James Clerk Maxwell, Bernhard Riemann, Hermann Grassmann, and Walther Ritz, developed this expression to find a fundamental expression of the force. Through differentiation, it can be shown that:
Coriolis force
In physics, the Coriolis force is an inertial or fictitious force that seems to act on objects that are in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the left of the motion of the object. In one with anticlockwise (or counterclockwise) rotation, the force acts to the right. Deflection of an object due to the Coriolis force is called the Coriolis effect. Though recognized previously by others, the mathematical expression for the Coriolis force appeared in an 1835 paper by French scientist Gaspard-Gustave de Coriolis, in connection with the theory of water wheels. Early in the 20th century, the term "Coriolis force" began to be used in connection with meteorology.
The Force
Astrophysicist Jeanne Cavelos says in "The Science of Star Wars" that the Force raises questions that scientists have long asked. She points out that the ancient Greeks explored the idea of a "fifth element" that permeated and connected everything in the universe, and that Isaac Newton proposed that the human brain might be able to trigger waves in the ether, giving humans psychic powers. Cavelos's sources are mostly skeptical about a "real world" explanation for the Force, but they explore ideas in areas such as quantum physics, parapsychology, and the notion of science so advanced that it appears magical. Explaining the Force is particularly difficult, Cavelos says, because "it does so many different things". Several scientists have said it is best not to try to explain how the Force works.