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  • Gravity | Britannica.com
    of the scientific method His formulation of circular inertia the gravity in mechanics the universal force of attraction acting between all matter It is by far the weakest known force in nature and thus plays no role in determining the internal properties of everyday matter On the other hand through its long reach and gravity centre of in physics imaginary point in a body of matter where for convenience in certain calculations the total weight of the body may be thought to be concentrated The concept is sometimes useful in designing static structures e g buildings and bridges Lagrangian point in astronomy a point in space at which a small body under the gravitational influence of two large ones will remain approximately at rest relative to them The existence of such points was deduced by the French mathematician and astronomer Joseph Louis Maclaurin Colin Scottish mathematician who developed and extended Sir Isaac Newton s work in calculus geometry and gravitation A child prodigy he entered the University of Glasgow at age 11 At the age of 19 he was elected a professor of mathematics at Marischal mascon a region of excess gravitational attraction on the surface of the Moon The word is a contraction of mass concentration Mascons were first identified by the observation of small anomalies in the orbits of Lunar Orbiter spacecraft launched in 1966 67 Mendenhall Thomas Corwin American physicist and meteorologist the first to propose the use of a ring pendulum for measuring absolute gravity Mendenhall was a professor at Ohio State University Columbus in 1873 78 and from 1881 until he was named professor emeritus in 1884 Newton Sir Isaac English physicist and mathematician who was the culminating figure of the scientific revolution of the 17th century In optics his discovery of the composition of

    Original URL path: http://www.britannica.com/topic-browse/Physics/Gravity (2016-02-13)
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  • Light | Britannica.com
    French physicist who pioneered in optics and did much to establish the wave theory of light advanced by English physicist Thomas Young Beginning in 1804 Fresnel served as an engineer building roads in various departments of France He began his research Gullstrand Allvar Swedish ophthalmologist recipient of the 1911 Nobel Prize for Physiology or Medicine for his research on the eye as a light refracting apparatus Gullstrand studied in Uppsala Vienna and Stockholm earning a doctorate in 1890 He became professor Hooke Robert English physicist who discovered the law of elasticity known as Hooke s law and who did research in a remarkable variety of fields In 1655 Hooke was employed by Robert Boyle to construct the Boylean air pump Five years later Hooke discovered his Kramers Hendrik Anthony Dutch physicist who with Ralph de Laer Kronig derived important equations relating the absorption to the dispersion of light He also predicted 1924 the existence of the Raman effect an inelastic scattering of light and showed 1927 that the complex Lambert Johann Heinrich Swiss German mathematician astronomer physicist and philosopher who provided the first rigorous proof that π the ratio of a circle s circumference to its diameter is irrational meaning that it cannot be expressed as the quotient of two integers Land Edwin Herbert American inventor and physicist whose one step process for developing and printing photographs culminated in a revolution in photography unparalleled since the advent of roll film While a student at Harvard University Land became interested in polarized Lebedev Pyotr Nikolayevich Russian physicist who experimentally proved that light exerts a mechanical pressure on material bodies Lebedev received his doctorate 1891 from the University of Strasburg in Germany The next year he began teaching physics at Moscow State University light electromagnetic radiation that can be detected by the

    Original URL path: http://www.britannica.com/topic-browse/Physics/Light (2016-02-13)
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  • Magnetism | Britannica.com
    magnetic mineral magnetite diamagnetism kind of magnetism characteristic of materials that line up at right angles to a nonuniform magnetic field and that partly expel from their interior the magnetic field in which they are placed First observed by S J Brugmans 1778 in bismuth and antimony electromagnet device consisting of a core of magnetic material surrounded by a coil through which an electric current is passed to magnetize the core An electromagnet is used wherever controllable magnets are required as in contrivances in which the magnetic flux ferrimagnetism type of permanent magnetism that occurs in solids in which the magnetic fields associated with individual atoms spontaneously align themselves some parallel or in the same direction as in ferromagnetism and others generally antiparallel or paired ferromagnetism physical phenomenon in which certain electrically uncharged materials strongly attract others Two materials found in nature lodestone or magnetite an oxide of iron Fe 3 O 4 and iron have the ability to acquire such attractive powers and they Gilbert William pioneer researcher into magnetism who became the most distinguished man of science in England during the reign of Queen Elizabeth I Educated as a physician Gilbert settled in London and began to practice in 1573 His principal work De Magnete Magneticisque hysteresis lagging of the magnetization of a ferromagnetic material such as iron behind variations of the magnetizing field When ferromagnetic materials are placed within a coil of wire carrying an electric current the magnetizing field or magnetic field strength Kapitsa Pyotr Leonidovich Soviet physicist who invented new machines for liquefaction of gases and in 1937 discovered the superfluidity of liquid helium He was a corecipient of the 1978 Nobel Prize for Physics for his basic inventions and discoveries in the area of low temperature magnet any material capable of attracting iron and

    Original URL path: http://www.britannica.com/topic-browse/Physics/Magnetism (2016-02-13)
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  • Matter | Britannica.com
    an acid or a base the acid or base itself not being consumed in the reaction The catalytic reaction may be acid specific acid catalysis as in the case of decomposition of the sugar sucrose into acid base reaction a type of chemical process typified by the exchange of one or more hydrogen ions H between species that may be neutral molecules such as water H 2 O or acetic acid CH 3 CO 2 H or electrically charged ions such as ammonium NH 4 hydroxide acoustic impedance absorption of sound in a medium equal to the ratio of the sound pressure at a boundary surface to the sound flux flow velocity of the particles or volume velocity times area through the surface In analogy to electrical circuit theory pressure corresponds actinium Ac radioactive chemical element in Group 3 IIIb of the periodic table atomic number 89 Actinium was discovered 1899 by French chemist André Louis Debierne in pitchblende residues left after French physicists Pierre and Marie Curie had extracted actinoid element any of a series of 15 consecutive chemical elements in the periodic table from actinium to lawrencium atomic numbers 89 103 As a group they are significant largely because of their radioactivity Although several members of the group including uranium action in theoretical physics an abstract quantity that describes the overall motion of a physical system Motion in physics may be described from at least two points of view the close up view and the panoramic view The close up view involves an instant by instant addition reaction any of a class of chemical reactions in which an atom or group of atoms is added to a molecule Addition reactions are typical of unsaturated organic compounds i e alkenes which contain a carbon to carbon double bond and alkynes which have a carbon to carbon adhesive any substance that is capable of holding materials together in a functional manner by surface attachment that resists separation Adhesive as a general term includes cement mucilage glue and paste terms that are often used interchangeably for any adiabatic demagnetization process by which the removal of a magnetic field from certain materials serves to lower their temperature This procedure proposed by chemists Peter Debye 1926 and William Francis Giauque independently 1927 provides a means for cooling an already adsorption capability of all solid substances to attract to their surfaces molecules of gases or solutions with which they are in contact Solids that are used to adsorb gases or dissolved substances are called adsorbents the adsorbed molecules are usually referred albedo fraction of light that is reflected by a body or surface It is commonly used in astronomy to describe the reflective properties of planets satellites and asteroids Albedo is usually differentiated into two general types normal albedo and bond albedo alcohol any of a class of organic compounds characterized by one or more hydroxyl OH groups attached to a carbon atom of an alkyl group hydrocarbon chain Alcohols may be considered as

    Original URL path: http://www.britannica.com/topic-browse/Physics/Matter (2016-02-13)
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  • Mechanics | Britannica.com
    German Auf bau prin zip building up principle rationalization of the distribution of electrons among energy levels in the ground most stable states of atoms The principle formulated by the Danish physicist Niels Bohr about 1920 is an austausch coefficient in fluid mechanics particularly in its applications to meteorology and oceanography the proportionality between the rate of transport of a component of a turbulent fluid and the rate of change of density of the component In this context the term ballistics science of the propulsion flight and impact of projectiles It is divided into several disciplines Internal and external ballistics respectively deal with the propulsion and the flight of projectiles The transition between these two regimes is Boltzmann Ludwig Eduard physicist whose greatest achievement was in the development of statistical mechanics which explains and predicts how the properties of atoms such as mass charge and structure determine the visible properties of matter such as viscosity thermal celestial mechanics in the broadest sense the application of classical mechanics to the motion of celestial bodies acted on by any of several types of forces By far the most important force experienced by these bodies and much of the time the only important force is Ceva Giovanni Italian mathematician physicist and hydraulic engineer best known for the geometric theorem bearing his name concerning straight lines that intersect at a common point when drawn through the vertices of a triangle Most details of Ceva s early life Coriolis Gustave Gaspard French engineer and mathematician who first described the Coriolis force an effect of motion on a rotating body of paramount importance to meteorology ballistics and oceanography An assistant professor of analysis and mechanics at the École Polytechnique Delaunay Charles Eugène French mathematician and astronomer whose theory of lunar motion advanced the development of planetary motion theories Delaunay was educated as an engineer at the École des Mines from 1836 becoming an engineer in 1843 and chief engineer in 1858 He dynamics branch of physical science and subdivision of mechanics that is concerned with the motion of material objects in relation to the physical factors that affect them force mass momentum energy A brief treatment of dynamics follows For full treatment Ehrenfest Paul Austrian theoretical physicist who helped clarify the foundations of quantum theory and statistical mechanics Ehrenfest studied with Ludwig Boltzmann at the University of Vienna where he received his doctorate in 1904 Ehrenfest and his wife Russian electrogasdynamics study of the forces produced by the motion of electrically charged particles ions carried by an insulating gas flowing through an electric field See also magnetohydrodynamic power generator electronic configuration the arrangement of electrons in energy levels around an atomic nucleus According to the older shell atomic model electrons occupy several levels from the first shell nearest the nucleus K through the seventh shell Q farthest from the nucleus In electroweak theory in physics the theory that describes both the electromagnetic force and the weak force Superficially these forces appear quite different The weak force

    Original URL path: http://www.britannica.com/topic-browse/Physics/Mechanics (2016-02-13)
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  • Nobel Prize in Physics | Britannica.com
    Edward Victor British winner of the Nobel Prize for Physics in 1947 for his discovery of the so called Appleton layer of the ionosphere which is a dependable reflector of radio waves and as such is useful in communication Other ionospheric layers reflect radio waves Bardeen John American physicist who was cowinner of the Nobel Prize for Physics in both 1956 and 1972 He shared the 1956 prize with William B Shockley and Walter H Brattain for their joint invention of the transistor With Leon N Cooper and John R Schrieffer Barkla Charles Glover British physicist who was awarded the Nobel Prize for Physics in 1917 for his work on X ray scattering which occurs when X rays pass through a material and are deflected by the atomic electrons This technique proved to be particularly useful in the Basov Nikolay Gennadiyevich Soviet physicist one of the founders of quantum electronics and a corecipient of the Nobel Prize for Physics in 1964 with Aleksandr Mikhaylovich Prokhorov of the Soviet Union and Charles H Townes of the United States for research leading to the Becquerel Henri French physicist who discovered radioactivity through his investigations of uranium and other substances In 1903 he shared the Nobel Prize for Physics with Pierre and Marie Curie He was a member of a scientific family extending through several generations Bednorz J Georg German physicist who along with Karl Alex Müller was awarded the 1987 Nobel Prize for Physics for their joint discovery of superconductivity in certain substances at temperatures higher than had previously been thought attainable Bednorz graduated Binnig Gerd German born physicist who shared with Heinrich Rohrer half of the 1986 Nobel Prize for Physics for their invention of the scanning tunneling microscope Ernst Ruska won the other half of the prize Binnig graduated from Johann Wolfgang Goethe University Blackett Patrick M S Baron Blackett of Chelsea winner of the Nobel Prize for Physics in 1948 for his discoveries in the field of cosmic radiation which he accomplished primarily with cloud chamber photographs that revealed the way in which a stable atomic nucleus can be disintegrated by bombarding Bloch Felix Swiss born American physicist who shared with E M Purcell the Nobel Prize for Physics in 1952 for developing the nuclear magnetic resonance method of measuring the magnetic field of atomic nuclei Bloch s doctoral dissertation University of Leipzig Bloembergen Nicolaas Dutch born American physicist corecipient with Arthur Leonard Schawlow of the United States and Kai Manne Börje Siegbahn of Sweden of the 1981 Nobel Prize for Physics for their revolutionary spectroscopic studies of the interaction of electromagnetic Bohr Aage N Danish physicist who shared the 1975 Nobel Prize for Physics with Ben R Mottelson and James Rainwater for their work in determining the asymmetrical shapes of certain atomic nuclei Bohr was educated at the University of Copenhagen where he received Bohr Niels Danish physicist who is generally regarded as one of the foremost physicists of the 20th century He was the first to apply

    Original URL path: http://www.britannica.com/topic-browse/Physics/Nobel-Prize-in-Physics (2016-02-13)
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  • Optics | Britannica.com
    The hole atmospheric optics study of optical characteristics and phenomena associated with the interaction of visible sunlight with atmospheric gases particulates and water vapour Refraction diffraction Rayleigh scattering and polarization of light are within the compass Bacon Roger English Franciscan philosopher and educational reformer who was a major medieval proponent of experimental science Bacon studied mathematics astronomy optics alchemy and languages He was the first European to describe in detail the process of making Barlow Peter optician and mathematician who invented two varieties of achromatic non colour distorting telescope lenses known as Barlow lenses Self educated he became assistant mathematics master at the Royal Military Academy Woolwich in 1801 He published binocular optical instrument usually handheld for providing a magnified stereoscopic view of distant objects consisting of two similar telescope s one for each eye mounted on a single frame A single thumbwheel may control the focus of both telescopes simultaneously Brewster Sir David Scottish physicist noted for his experimental work in optics and polarized light i e light in which all waves lie in the same plane When light strikes a reflective surface at a certain angle called the polarizing angle the reflected light becomes Buridan Jean Aristotelian philosopher logician and scientific theorist in optics and mechanics After studies in philosophy at the University of Paris under the nominalist thinker William of Ockham Buridan was appointed professor of philosophy there He served Campani Giuseppe Italian optical instrument maker who invented a lens grinding lathe Of peasant origin Campani as a young man studied in Rome There he learned to grind lenses and with his two brothers invented a silent night clock that when presented to Pope Alexander chromatic aberration colour distortion in an image viewed through a glass lens Because the refractive index of glass varies with wavelength every property of a lens that depends on its refractive index also varies with wavelength including the focal length the image collimator device for changing the diverging light or other radiation from a point source into a parallel beam This collimation of the light is required to make specialized measurements in spectroscopy and in geometric and physical optics An optical collimator contact lens thin artificial lens worn on the surface of the eye to correct refractive defects of vision The first contact lens made of glass was developed by Adolf Fick in 1887 to correct irregular astigmatism The early lenses however were uncomfortable and diffraction grating component of optical devices consisting of a surface ruled with close equidistant and parallel lines for the purpose of resolving light into spectra A grating is said to be a transmission or reflection grating according to whether it is transparent diopter in optics unit of magnifying power of a lens or lens system Because the power of a lens is proportional to unity one divided by the focal length see lens the power of a lens in diopters is numerically equal to 1 m divided by the focal length in Divini Eustachio Italian scientist one

    Original URL path: http://www.britannica.com/topic-browse/Physics/Optics (2016-02-13)
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  • Quantum Mechanics | Britannica.com
    of antiparticles In 1933 he electronic configuration the arrangement of electrons in energy levels around an atomic nucleus According to the older shell atomic model electrons occupy several levels from the first shell nearest the nucleus K through the seventh shell Q farthest from the nucleus In electroweak theory in physics the theory that describes both the electromagnetic force and the weak force Superficially these forces appear quite different The weak force acts only across distances smaller than the atomic nucleus while the electromagnetic force can energy state in physics any discrete value from a set of values of total energy for a subatomic particle confined by a force to a limited space or for a system of such particles such as an atom or a nucleus A particular hydrogen atom for example may exist in excitation in physics the addition of a discrete amount of energy called excitation energy to a system such as an atomic nucleus an atom or a molecule that results in its alteration ordinarily from the condition of lowest energy ground state to one of Fermi level a measure of the energy of the least tightly held electrons within a solid named for Enrico Fermi the physicist who first proposed it It is important in determining the electrical and thermal properties of solids The value of the Fermi level at absolute Feynman diagram a graphical method of representing the interactions of elementary particles invented in the 1940s and 50s by the American theoretical physicist Richard P Feynman Introduced during the development of the theory of quantum electrodynamics as an aid Feynman Richard P American theoretical physicist who was widely regarded as the most brilliant influential and iconoclastic figure in his field in the post World War II era Feynman remade quantum electrodynamics the theory of the interaction between light and matter and Fock Vladimir Aleksandrovich Russian mathematical physicist who made seminal contributions to quantum mechanics and the general theory of relativity Fock became progressively deaf at a young age because of injuries sustained during military service in World War I In 1922 he graduated Franck Hertz experiment in physics first experimental verification of the existence of discrete energy states in atoms performed 1914 by the German born physicists James Franck and Gustav Hertz Franck and Hertz directed low energy electrons through a gas enclosed in an gauge theory class of quantum field theory a mathematical theory involving both quantum mechanics and Einstein s special theory of relativity that is commonly used to describe subatomic particles and their associated wave fields In a gauge theory there is a group Heisenberg Werner German physicist and philosopher who discovered 1925 a way to formulate quantum mechanics in terms of matrices For that discovery he was awarded the Nobel Prize for Physics for 1932 In 1927 he published his uncertainty principle upon which he built Jordan Pascual German theoretical physicist who was one of the founders of quantum mechanics and quantum field theory Jordan received a doctorate 1924 from

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