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This article is about the scientific notion. For other uses, see Gravitation (disambiguation).

Gravitation is a natural phenomenon by which all objects with mass attract each other, and is one of the fundamental forces of physics. A phenomenon (from Greek φαινόμενoν, pl φαινόμενα - phenomena) is any observable occurrence Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object In Physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other and which cannot be explained in terms In everyday life, gravitation is most commonly thought of as the agency that gives objects weight. In the Physical sciences weight is a Measurement of the gravitational Force acting on an object It is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth, for the formation of tides; for convection (by which hot fluids rise); for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena that we observe. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood Convection in the most general terms refers to the movement of molecules within Fluids (i Gravitation is also the reason for the very existence of the Earth, the Sun, and most macroscopic objects in the universe; without it, matter would not have coalesced into these large masses and life, as we know it, would not exist. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The Sun (Sol is the Star at the center of the Solar System. The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy Life is a state that distinguishes Organisms from non-living objects such as non-life and dead organisms being manifested by growth through Metabolism

Modern physics describes gravitation using the general theory of relativity, but the much simpler Newton's law of universal gravitation provides an excellent approximation in most cases. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass

The terms gravitation and gravity are mostly interchangeable in everyday use, but in scientific usage a distinction may be made. "Gravitation" is a general term describing the attractive influence that all objects with mass exert on each other, while "gravity" specifically refers to a force that is supposed in some theories (such as Newton's) to be the cause of this attraction. In Physics, a force is whatever can cause an object with Mass to Accelerate. By contrast, in general relativity gravitation is due to spacetime curvatures that cause inertially moving objects to accelerate towards each other. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 The vis insita or innate force of matter is a power of resisting by which every body as much as in it lies endeavors to preserve in its present state whether it be of rest or of moving

Gravitation keeps the planets in orbit about the Sun. (Not to scale)
Gravitation keeps the planets in orbit about the Sun. (Not to scale)

Contents

History of gravitational theory

Main article: History of gravitational theory

Early history

Efforts to understand gravity began in ancient times. In Physics, theories of gravitation postulate mechanisms of interaction governing the movements of bodies with mass Philosophers in ancient India explained the phenomenon from the 8th century BC. The term Indian philosophy (Sanskrit Darshanas) may refer to any of several traditions of philosophical thought that originated in the Indian subcontinent The History of science in early cultures refers to the study of Protoscience in Ancient history, prior to the development of Science in the Middle [1] According to Kanada, founder of the Vaisheshika school, "Weight causes falling; it is imperceptible and known by inference. Kanada ( Sanskrit: कणाद; also transliterated as Canada as well as other forms was a Hindu sage who founded the philosophical Vaisheshika, or Vaiśeṣika, (Sanskrit वैशॆषिक) is one of the six Hindu schools of Philosophy (orthodox Vedic systems Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Inference is the act or process of deriving a Conclusion based solely on what one already knows "[2]

In the 4th century BC, the Greek philosopher Aristotle believed that there was no effect without a cause, and therefore no motion without a force. Ancient Greek philosophy focused on the role of Reason and Inquiry. Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great. A result is the final consequence of a Sequence of actions or events (broadly incidents and accidents expressed qualitatively or quantitatively being a loss injury disadvantage Causality (but not causation) denotes a necessary relationship between one event (called cause and another event (called effect) which is the direct consequence In Physics, motion means a constant change in the location of a body In Physics, a force is whatever can cause an object with Mass to Accelerate. He hypothesized that everything tried to move towards its proper place in the crystalline spheres of the heavens, and that physical bodies fell toward the center of the Earth in proportion to their weight. The celestial spheres or celestial orbs were the fundamental celestial entities of the cosmological celestial mechanics first invented by Eudoxus, and developed by Aristotle EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 In the Physical sciences weight is a Measurement of the gravitational Force acting on an object

Brahmagupta, in the Brahmasphuta Siddhanta (AD 628), responded to critics of the heliocentric system of Aryabhata (AD 476–550) stating that "all heavy things are attracted towards the center of the earth" and that "all heavy things fall down to the earth by a law of nature, for it is the nature of the earth to attract and to keep things, as it is the nature of water to flow, that of fire to burn, and that of wind to set in motion. Brahmagupta ( (598–668 was an Indian mathematician and astronomer. The main work of Brahmagupta, Brahmasphuta-siddhanta (The Opening of the Universe, written in the year 628, contains some remarkably advanced ideas including In Astronomy, heliocentrism is the theory that the Sun is at the center of the Solar System. Āryabhaṭa ( Devanāgarī: आर्यभट (AD 476 &ndash 550 is the first in the line of great mathematician-astronomers from the classical age of Indian mathematics . . The earth is the only low thing, and seeds always return to it, in whatever direction you may throw them away, and never rise upwards from the earth. "[3][4]

In the 9th century, the eldest Banū Mūsā brother, Muhammad ibn Musa, in his Astral Motion and The Force of Attraction, hypothesized that there was a force of attraction between heavenly bodies,[5] foreshadowing Newton's law of universal gravitation. The Banū Mūsā brothers (بنو موسى "Sons of Mūsā" were three 9th century Persian Scholars of Baghdad, active in the House Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass [6] In the 1000s, the Persian scientist Ibn al-Haytham (Alhacen), in the Mizan al-Hikmah, discussed the theory of attraction between masses, and it seems that he was aware of the magnitude of acceleration due to gravity. layout and formatting it should ensure no clashes with the top of the infobox TemplateInfobox Muslim scholars --> ( Arabic: ابو علی، حسن بن حسن بن هيثم Latinized Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object The magnitude of a mathematical object is its size a property by which it can be larger or smaller than other objects of the same kind in technical terms an Ordering [7] In 1121, Al-Khazini, in The Book of the Balance of Wisdom, differentiated between force, mass, and weight,[8] and discovered that gravity varies with the distance from the centre of the Earth,[9] though he believed that the weight of heavy bodies increase as they are farther from the centre of the Earth. Abd al-Rahman al-Khazini ( عبدالرحمن الخزيني) (flourished 1115–1130 was a Muslim scientist, physicist, astronomer, biologist In Physics, a force is whatever can cause an object with Mass to Accelerate. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object In the Physical sciences weight is a Measurement of the gravitational Force acting on an object [10] All these early attempts at trying to explain the force of gravity were philosophical in nature and it would be Isaac Newton that gave the first correct description of gravity. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements Gravitation is a natural Phenomenon by which objects with Mass attract one another

Scientific revolution

Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th century and early 17th century. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher In his famous (though probably apocryphal) experiment dropping balls from the Tower of Pisa, and later with careful measurements of balls rolling down inclines, Galileo showed that gravitation accelerates all objects at the same rate. The Leaning Tower of Pisa (Torre pendente di Pisa or simply The Tower of Pisa (it La Torre di Pisa is the Campanile, or freestanding bell tower of the This article deals with the physical structure For related terms see Canal inclined plane, Cable railway, Funicular, or Fixed-wing This was a major departure from Aristotle's belief that heavier objects are accelerated faster. [11] (Galileo correctly postulated air resistance as the reason that lighter objects may fall more slowly in an atmosphere. ) Galileo's work set the stage for the formulation of Newton's theory of gravity.

Newton's theory of gravitation

Main article: Newton's law of universal gravitation

In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements The Philosophiæ Naturalis Principia Mathematica ( Latin: "mathematical principles of natural philosophy" often Principia In Physics, an inverse-square law is any Physical law stating that some physical Quantity or strength is inversely proportional In his own words, “I deduced that the forces which keep the planets in their orbs must be reciprocally as the squares of their distances from the centers about which they revolve; and thereby compared the force requisite to keep the Moon in her orb with the force of gravity at the surface of the Earth; and found them answer pretty nearly. ”

Newton's theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted by the actions of the other planets. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. Calculations by John Couch Adams and Urbain Le Verrier both predicted the general position of the planet, and Le Verrier's calculations are what led Johann Gottfried Galle to the discovery of Neptune. John Couch Adams ( June 5 1819 &ndash January 21, 1892) was a British Mathematician and Astronomer Urbain Jean Joseph Le Verrier ( March 11, 1811 &ndash September 23, 1877) was a French Mathematician who specialized in Celestial Johann Gottfried Galle ( June 9, 1812 &ndash July 10, 1910) was a German Astronomer at the Berlin Observatory

Ironically, it was another discrepancy in a planet's orbit that helped to point out flaws in Newton's theory. By the end of the 19th century, it was known that the orbit of Mercury could not be accounted for entirely under Newton's theory, but all searches for another perturbing body (such as a planet orbiting the Sun even closer than Mercury) had been fruitless. The Sun (Sol is the Star at the center of the Solar System. The issue was resolved in 1915 by Albert Einstein's new General Theory of Relativity, which accounted for the discrepancy in Mercury's orbit. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916

Although Newton's theory has been superseded, most modern non-relativistic gravitational calculations are still made using Newton's theory because it is a much simpler theory to work with than General Relativity, and gives sufficiently accurate results for most applications. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916

General relativity

Main article: Introduction to general relativity

In general relativity, the effects of gravitation are ascribed to spacetime curvature instead of a force. General relativity (GR is a Theory of Gravitation that was developed by Albert Einstein between 1907 and 1915 General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS In Mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry The starting point for general relativity is the equivalence principle, which equates free fall with inertial motion. The equivalence principle The issue that this creates is that free-falling objects can accelerate with respect to each other. In Newtonian physics, no such acceleration can occur unless at least one of the objects is being operated on by a force (and therefore is not moving inertially). Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects

To deal with this difficulty, Einstein proposed that spacetime is curved by matter, and that free-falling objects are moving along locally straight paths in curved spacetime. (This type of path is called a geodesic. In General relativity, Geodesics generalize the notion of "straight lines" to curved Spacetime. ) More specifically, Einstein discovered the field equations of general relativity, which relate the presence of matter and the curvature of spacetime and are named after him. A field equation is an equation in a Physical theory that describes how a Fundamental force (or a combination of such forces interacts with Matter The Einstein field equations are a set of 10 simultaneous, non-linear, differential equations. The Einstein field equations ( EFE) or Einstein's equations are a set of ten equations in Einstein 's theory of General relativity in which the In Mathematics simultaneous equations are a set of Equations containing multiple variables This article describes the use of the term nonlinearity in mathematics A differential equation is a mathematical Equation for an unknown function of one or several variables that relates the values of the The solutions of the field equations are the components of the metric tensor of spacetime. This article discusses metrics in General relativity, for a discussion of metrics in general see Metric tensor. A metric tensor describes a geometry of spacetime. The geodesic paths for a spacetime are calculated from the metric tensor.

Notable solutions of the Einstein field equations include:

General relativity has enjoyed much success because of how its predictions of phenomena which are not called for by the theory of gravity have been regularly confirmed. For example:

Gravity and quantum mechanics

Main articles: Graviton and Quantum gravity

Several decades after the discovery of general relativity it was realized that general relativity is incompatible with quantum mechanics. In Physics, the graviton is a hypothetical Elementary particle, a Boson to be exact that mediates the force of Gravity in the framework Quantum gravity is the field of Theoretical physics attempting to unify Quantum mechanics, which describes three of the fundamental forces of nature Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons [12] It is possible to describe gravity in the framework of quantum field theory like the other fundamental forces, with the attractive force of gravity arises due to exchange of virtual gravitons, in the same way as the electromagnetic force arises from exchange of virtual photons. In quantum field theory (QFT the forces between particles are mediated by other particles In Physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other and which cannot be explained in terms In Physics, a virtual particle is a particle that exists for a limited time and space introducing uncertainty in their energy and momentum due to the Heisenberg Uncertainty In Physics, the graviton is a hypothetical Elementary particle, a Boson to be exact that mediates the force of Gravity in the framework In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena [13][14] This reproduces general relativity in the classical limit. The classical limit is the ability of a physical theory to approximate or "recover" Classical mechanics when considered over special values of its parameters However, this approach fails at short distances of the order of the Planck length,[15] where a more complete theory of quantum gravity (or a new approach to quantum mechanics) is required. The Planck length, denoted by \scriptstyle\ell_P \, is the unit of Length approximately 1 Quantum gravity is the field of Theoretical physics attempting to unify Quantum mechanics, which describes three of the fundamental forces of nature Many believe the complete theory to be string theory,[16] or more currently M Theory. String theory is a still-developing scientific approach to Theoretical physics, whose original building blocks are one-dimensional extended objects called strings In Theoretical physics, M-theory is a new limit of String theory in which 11 dimensions of Spacetime may be identified

Specifics

Earth's gravity

Main article: Earth's gravity

Every planetary body (including the Earth) is surrounded by its own gravitational field, which exerts an attractive force on all objects. Earth's gravity, denoted by g, refers to the Gravitational attraction that the Earth exerts on objects on or near its surface Assuming a spherically symmetrical planet (a reasonable approximation), the strength of this field at any given point is proportional to the planetary body's mass and inversely proportional to the square of the distance from the center of the body.

The strength of the gravitational field is numerically equal to the acceleration of objects under its influence, and its value at the Earth's surface, denoted g, is approximately expressed below as the standard average. Standard gravity, usually denoted by g 0 or g n is the nominal acceleration due to gravity at the Earth's surface at sea level

g = 9.8 \frac{m}{s^2} = 32.2 \frac{ft}{s^2}

This means that, ignoring air resistance, an object falling freely near the earth's surface increases its velocity with 9.8\tfrac{m}{s} (32.2\tfrac{ft}{s} or 22 mph) for each second of its descent. Thus, an object starting from rest will attain a velocity of 9.8\tfrac{m}{s} (32.2\tfrac{ft}{s}) after one second, 19.6\tfrac{m}{s} (64\tfrac{ft}{s}) after two seconds, and so on, adding 9.8\tfrac{m}{s} to each resulting velocity. According to Newton's 3rd Law, the Earth itself experiences an equal and opposite force to that acting on the falling object, meaning that the Earth also accelerates towards the object. However, because the mass of the Earth is huge, the acceleration of the Earth by this same force is negligible, when measured relative to the system's center of mass.

Equations for a falling body

Ball falling freely under gravity. See text for description.
Ball falling freely under gravity. See text for description.
Main article: Equations for a falling body

The kinematical and dynamical equations describing the trajectories of falling bodies are considerably simpler if the gravitational force is assumed constant. Under normal earth-bound conditions when objects move owing to a constant Gravitational Force a set of dynamical equations describe the resultant Trajectories This assumption is reasonable for objects falling to Earth over the relatively short vertical distances of our everyday experience, but does not hold over larger distances, such as spacecraft trajectories, since the acceleration due to Earth's gravity is much smaller at large distances. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001

Under an assumption of constant gravity, Newton’s law of gravitation simplifies to F = mg, where m is the mass of the body and g is a constant vector with an average magnitude of 9. Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 81 m/s². The acceleration due to gravity is equal to this g. An initially-stationary object which is allowed to fall freely under gravity drops a distance which is proportional to the square of the elapsed time. The image on the right, spanning half a second, was captured with a stroboscopic flash at 20 flashes per second. During the first 1/20th of a second the ball drops one unit of distance (here, a unit is about 12 mm); by 2/20ths it has dropped at total of 4 units; by 3/20ths, 9 units and so on.

Under the same constant gravity assumptions, the potential energy, Ep, of a body at height h is given by Ep = mgh (or Ep = Wh, with W meaning weight). Potential energy can be thought of as Energy stored within a physical system This expression is valid only over small distances h from the surface of the Earth. Similarly, the expression h = \tfrac{v^2}{2g} for the maximum height reached by a vertically projected body with velocity v is useful for small heights and small initial velocities only. In case of large initial velocities we have to use the principle of conservation of energy to find the maximum height reached. This same expression can be solved for v to determine the velocity of an object dropped from a height h immediately before hitting the ground, v=\sqrt{2gh}, assuming negligible air resistance.

Gravity and astronomy

Main article: Gravitation (astronomy)

The discovery and application of Newton's law of gravity accounts for the detailed information we have about the planets in our solar system, the mass of the Sun, the distance to stars, quasars and even the theory of dark matter. In Astronomy, the discovery and application of Newton's law of gravity accounted for the detailed information we have about the planets in our solar system the mass of the sun A quasar (contraction of QUASi-stellAR radio source) is an extremely powerful and distant Active galactic nucleus. In Physics and cosmology, dark matter is hypothetical Matter that does not interact with the electromagnetic force but whose presence can be inferred from Although we have not traveled to all the planets nor to the Sun, we know their masses. These masses are obtained by applying the laws of gravity to the measured characteristics of the orbit. In space an object maintains its orbit because of the force of gravity acting upon it. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star Planets orbit stars, stars orbit galactic centers, galaxies orbit a center of mass in clusters, and clusters orbit in superclusters. The Galactic Center is the rotational center of the Milky Way Galaxy. A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter Superclusters are large groupings of smaller galaxy groups and clusters, and are among the largest structures of the Cosmos. The force of gravity is proportional to the mass of an object and inversely proportional to the square of the distance between the objects.

Gravitational radiation

Main article: Gravitational wave

In general relativity, gravitational radiation is generated in situations where the curvature of spacetime is oscillating, such as is the case with co-orbiting objects. In Physics, a gravitational wave is a Fluctuation in the Curvature of Spacetime which propagates as a wave, traveling outward from SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS The gravitational radiation emitted by the solar system is far too small to measure. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. However, gravitational radiation has been indirectly observed as an energy loss over time in binary pulsar systems such as PSR 1913+16. It is believed that neutron star mergers and black hole formation may create detectable amounts of gravitational radiation. A neutron star is a type of remnant that can result from the Gravitational collapse of a massive Star during a Type II, Type Ib or Type A black hole is a theoretical region of space in which the Gravitational field is so powerful that nothing not even Electromagnetic radiation (e Gravitational radiation observatories such as LIGO have been created to study the problem. For the Latvian holiday Ligo see Jāņi. LIGO stands for Laser Interferometer Gravitational-Wave Observatory. No confirmed detections have been made of this hypothetical radiation, but as the science behind LIGO is refined and as the instruments themselves are endowed with greater sensitivity over the next decade, this may change.

Anomalies and discrepancies

There are some observations that are not adequately accounted for, which may point to the need for better theories of gravity or perhaps be explained in other ways.

Alternative theories

Main article: Alternatives to general relativity

Historical alternative theories

Recent alternative theories

See also

Notes

References

  1. ^ Dick Teresi (2002), Lost Discoveries: The Ancient Roots of Modern Science - from the Babylonians to the Maya, Simon & Schuster, New York, ISBN 0-684-83718-8:

    "Two hundred years before Pythagoras, philosophers in northern India had understood that gravitation held the solar system together, and that therefore the sun, the most massive object, had to be at its centre. "Pythagoras of Samos" redirects here For the Samian statuary of the same name see Pythagoras (sculptor. "

  2. ^ S. Kak (2003). Subhash Kak (सुभाष काक Subhāṣ Kāk) (born March 26, 1947 in Srinagar, Kashmir) is an Indian American Indian Physics: Outline of Early History, p. 22. arXiv. The arXiv ( pronounced " Archive " as if the "X" were the Greek letter Chi, χ is an Archive for electronic Louisiana State University. Louisiana State University and Agricultural and Mechanical College, generally known as Louisiana State University or LSU, is a public, Coeducational
  3. ^ Brahmagupta (628 AD). Brahmagupta ( (598–668 was an Indian mathematician and astronomer. Brahmasphuta Siddhanta ("The Opening of the Universe"). The main work of Brahmagupta, Brahmasphuta-siddhanta (The Opening of the Universe, written in the year 628, contains some remarkably advanced ideas including
  4. ^ Al-Biruni (1030). Ta'rikh al-Hind (Indica).
  5. ^ K. A. Waheed (1978). Islam and The Origins of Modern Science, p. 27. Islamic Publication Ltd. , Lahore.
  6. ^ Robert Briffault (1938). Robert Briffault ( 1876 - 11 December 1948) was a French novelist historian social anthropologist and surgeon The Making of Humanity, p. 191.
  7. ^ Dr. Nader El-Bizri, "Ibn al-Haytham or Alhazen", in Josef W. Meri (2006), Medieval Islamic Civilization: An Encyclopaedia, Vol. II, p. 343-345, Routledge, New York, London. Routledge is a publisher of non-fiction academic books and journals
  8. ^ Donald Routledge Hill (1993), Islamic Science and Engineering, p. Donald Routledge Hill (1922–1994 was an Engineer and historian of science and technology. 61, Edinburgh University Press. Edinburgh University Press is a University publisher that is part of the University of Edinburgh in Edinburgh, Scotland. (cf. Salah Zaimeche PhD (2005), Merv, p. cf is an abbreviation for the Latin -derived (but also modern English) word confer, meaning "compare" or "consult" 5, Foundation for Science Technology and Civilization. )
  9. ^ Professor Mohammed Abattouy (2002). "The Arabic Science of weights: A Report on an Ongoing Research Project", The Bulletin of the Royal Institute for Inter-Faith Studies 4, p. 109-130.
  10. ^ N. Khanikoff, ed. and trans. (1858-1860), "Analysis and Extracts of . . . Book of the Balance of Wisdom, An Arabic Work on the Water-Balance, Written by 'Al-Khâzinî in the Twelfth Century", chap. 5, sect. 3. 1, Journal of the American Oriental Society 6, p. 36.
  11. ^ Galileo (1638), Two New Sciences, First Day Salviati speaks: "If this were what Aristotle meant you would burden him with another error which would amount to a falsehood; because, since there is no such sheer height available on earth, it is clear that Aristotle could not have made the experiment; yet he wishes to give us the impression of his having performed it when he speaks of such an effect as one which we see. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher The Discourses and Mathematical Demonstrations Relating to Two New Sciences ( Discorsi e dimostrazioni matematiche intorno a due nuove scienze, 1638 was Galileo's "
  12. ^ Randall, Lisa (2005). Warped Passages: Unraveling the Universe's Hidden Dimensions. Ecco. ISBN 0-06-053108-8.  
  13. ^ Feynman, R. P. ; Morinigo, F. B. , Wagner, W. G. , & Hatfield, B. (1995). Feynman lectures on gravitation. Addison-Wesley. ISBN 0201627345.  
  14. ^ Zee, A. (2003). Quantum Field Theory in a Nutshell. Princeton University Press. ISBN 0-691-01019-6.  
  15. ^ Randall, Lisa (2005). Warped Passages: Unraveling the Universe's Hidden Dimensions. Ecco. ISBN 0-06-053108-8.  
  16. ^ Greene, Brian (2000). The elegant universe: superstrings, hidden dimensions, and the quest for the ultimate theory. New York: Vintage Books. ISBN 0375708111.  
  17. ^ [1] Dark energy may just be a cosmic illusion New Scientist
  18. ^ [2] Wanted: Einstein Jr, Mar 6th 2008 The Economist

External links

PhysOrgcom is a web-based News site specializing in the Hard science subjects of Physics, Space and Earth Science, Electronics

Dictionary

gravitation

-noun

  1. (physics) the fundamental force of attraction that exists between all particles with mass in the universe. It is the weakest of the four forces, and possesses a gauge boson known as the graviton. See also gravity.
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