Inertia is the resistance an object has to a change in its state of motion. The principle of inertia is one of the fundamental principles of classical physics which are used to describe the motion of matter and how it is affected by applied forces. Sir Isaac Newton defined inertia in Definition 3 of his Philosophiae Naturalis Principia Mathematica, which states:^[1] This article or section is in need of attention from an expert on the subject. ... Inertia is the tendency of a body to maintain its state of rest or uniform motion unless acted upon by an external force. ... Classical physics is physics based on principles developed before the rise of quantum theory, usually including the special theory of relativity and general theory of relativity. ... This article or section is in need of attention from an expert on the subject. ... This article is about matter in physics and chemistry. ... In physics, a net force acting on a body causes that body to accelerate; that is, to change its velocity. ... Sir Isaac Newton FRS (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... Newtons own copy of his Principia, with handwritten corrections for the second edition. ...

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 uniformly forward in a right line.

In common usage, however, people may also use the term "inertia" to refer to an object's "amount of resistance to change in velocity" (which is quantified by its mass), and sometimes its momentum, depending on context (e.g. "this object has a lot of inertia"). The term "inertia" is more properly understood as a shorthand for "the principle of inertia as described by Newton in Newton's First Law of Motion which, expressed simply, says: "An object that is not subject to any outside forces moves at a constant velocity, covering equal distances in equal times along a straight-line path." In even simpler terms, inertia means "A body in motion tends to remain in motion, a body at rest tends to remain at rest." On the surface of the Earth the nature of inertia is often masked by the effects of friction which brings moving objects to rest relatively quickly unless they are coasting on wheels, well lubricated or perhaps falling or going downhill, being accelerated by gravity. This is what misled classical theorists such as Aristotle who believed objects moved only so long as force was being applied to them.^[2] For other uses, see Mass (disambiguation). ... This article is about momentum in physics. ... Newtons laws of motion are three scientific laws which Isaac Newton discovered concerning the behaviour of moving bodies. ... For other uses, see Friction (disambiguation). ... Lubrication occurs when opposing surfaces are separated by a lubricant film. ... For the card game, see Falling (game). ... Acceleration is the time rate of change of velocity and/or direction, and at any point on a velocity-time graph, it is given by the slope of the tangent to the curve at that point. ... Gravity is a force of attraction that acts between bodies that have mass. ...

History and development of the concept

Early understanding of motion

Prior to the Renaissance in the 15th century, the generally accepted theory of motion in Western philosophy was that proposed by Aristotle (around 335 BC to 322 BC), which stated that in the absence of an external motive power, all objects (on earth) would naturally come to rest in a state of no movement, and that moving objects only continue to move so long as there is a power inducing them to do so. Aristotle explained the continued motion of projectiles, which are separated from their projector, by the action of the surrounding medium which continues to move the projectile in some way.^[3] As a consequence, Aristotle concluded that such violent motion in a void was impossible for there would be nothing there to keep the body in motion against the resistance of its own gravity.^[4] Then in a statement regarded by Newton as expressing his Principia's first law of motion, Aristotle continued by asserting that a body in (non-violent) motion in a void would continue moving forever if externally unimpeded: This article is about the European Renaissance of the 14th-17th centuries. ... Western philosophy is a modern claim that there is a line of related philosophical thinking, beginning in ancient Greece (Greek philosophy) and the ancient Near East (the Abrahamic religions), that continues to this day. ... For other uses, see Aristotle (disambiguation). ...

[N]o one could say why a thing once set in motion should stop anywhere; for why should it stop here rather than here? So that a thing will either be at rest or must be moved ad infinitum, unless something more powerful gets in its way.^[5]

Despite its remarkable success and general acceptance, Aristotle's concept of motion was disputed on several occasions by notable philosophers over the nearly 2 millennia of its reign. For example, Lucretius (following, presumably, Epicurus) clearly stated that the 'default state' of matter was motion, not stasis.^[6] In the 6th century, John Philoponus criticized Aristotle's view, noting the inconsistency between Aristotle's discussion of projectiles, where the medium keeps projectiles going, and his discussion of the void, where the medium would hinder a body's motion. Philoponus proposed that motion was not maintained by the action of the surrounding medium but by some property implanted in the object when it was set in motion. This was not the modern concept of inertia, for there was still the need for a power to keep a body in motion.^[7] This view was strongly opposed by Averroës and many scholastic philosophers who supported Aristotle. However this view did not go unchallenged in the Islamic world, where Philoponus did have several supporters. Look up Ad infinitum in Wiktionary, the free dictionary. ... These pages contain the trends of millennia and centuries. ... Lucretius Titus Lucretius Carus (c. ... Epicure redirects here. ... It has been suggested that this article or section be merged with Joannes Philoponus. ... Averroes Averroes (Ibn Rushd) (1126 - December 10, 1198) was an Andalusian-Arab philosopher and physician, a master of philosophy and Islamic law, mathematics and medicine. ... Scholastic is the official student publication of the University of Notre Dame. ... During the Islamic Golden Age, usually dated from the 8th century to the 13th century,[1] engineers, scholars and traders of the Islamic world contributed enormously to the arts, agriculture, economics, industry, literature, navigation, philosophy, sciences, and technology, both by preserving and building upon earlier traditions and by adding many...

Chinese theories

Mozi (Chinese: 墨子; pinyin: Mòzǐ; ca. 470 BCE–ca. 390 BCE), a philosopher who lived in China during the Hundred Schools of Thought period (early Warring States Period), composed or collected his thought in the book Mozi, which contains the following sentence: 'The cessation of motion is due to the opposing force ... If there is no opposing force ... the motion will never stop. This is as true as that an ox is not a horse.' which, according to Joseph Needham, is a precursor to Newton's first law of motion. Mozi (Chinese: ; pinyin: ; Wade-Giles: Mo Tzu, Lat. ...

Islamic theories

This article or section may contain original research or unverified claims. Please improve the article by adding references. See the talk page for details. (March 2008)

Main article: Islamic science - Mechanics

Several Muslim scientists from the medieval Islamic world wrote Arabic treatises on theories of motion. In the early 11th century, the Islamic scientist Ibn al-Haytham (Arabic:ابن الهيثم) (Latinized as Alhacen) experimented on the motion of a body and discovered that a body moves perpetually unless an external force stops it or changes its direction of motion. Alhacen's theory of motion was thus similar to the modern law of inertia (now known as Newton's first law of motion) later stated by Galileo Galilei in the 16th century.^[8] Image File history File links Emblem-important. ... In the history of science, Islamic science refers to the science developed under the Islamic civilisation between the 8th and 15th centuries (the Islamic Golden Age). ... In the history of science, Islamic science refers to the science developed under the Islamic civilisation between the 8th and 15th centuries (the Islamic Golden Age). ... During the Islamic Golden Age, usually dated from the 8th century to the 13th century,[1] engineers, scholars and traders of the Islamic world contributed enormously to the arts, agriculture, economics, industry, literature, navigation, philosophy, sciences, and technology, both by preserving and building upon earlier traditions and by adding many... Arabic redirects here. ... This article or section is in need of attention from an expert on the subject. ... (Arabic: أبو علي الحسن بن الحسن بن الهيثم, Latinized: Alhacen or (deprecated) Alhazen) (965 – 1039), was an Arab[1] Muslim polymath[2][3] who made significant contributions to the principles of optics, as well as to anatomy, astronomy, engineering, mathematics, medicine, ophthalmology, philosophy, physics, psychology, visual perception, and to science in general with his introduction of the... This article is considered orphaned, since there are very few or no other articles that link to this one. ... In the scientific method, an experiment (Latin: ex- periri, of (or from) trying) is a set of observations performed in the context of solving a particular problem or question, to retain or falsify a hypothesis or research concerning phenomena. ... This article or section should include material from Parallel Path See also Perpetuum mobile as a musical term Perpetual motion machines (the Latin term perpetuum mobile is not uncommon) are a class of hypothetical machines which would produce useful energy in a way science cannot explain (yet). ... For other uses, see Force (disambiguation). ... Newtons First and Second laws, in Latin, from the original 1687 edition of the Principia Mathematica. ... Galileo redirects here. ...

Alhacen's contemporary, the Persian scientist Ibn Sina (Latinized as Avicenna), developed an elaborate theory of motion, in which he made a distinction between the inclination and force of a projectile, and concluded that motion was a result of an inclination (mayl) transferred to the projectile by the thrower, and that projectile motion in a vacuum would not cease.^[9] He viewed inclination as a permanent force whose effect is dissipated by external forces such as air resistance.^{[10] [9]} Avicenna also referred to mayl to as being proportional to weight times velocity, which was similar to Newton's theory of momentum.^[11] Avicenna's concept of mayl was later used in Jean Buridan's theory of impetus. This article is about the Persian people, an ethnic group found mainly in Iran. ... (Persian: ابن سينا) (c. ... For the science fiction novella by William Shunn, see Inclination (novella). ... For other uses, see Force (disambiguation). ... A projectile is any object sent through space by the application of a force. ... A trajectory is an imagined trace of positions followed by an object moving through space. ... For a solid object moving through a fluid or gas, drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid flow. ... For other uses, see Weight (disambiguation). ... This article is about velocity in physics. ... This article is about momentum in physics. ... Jean Buridan, in Latin Joannes Buridanus (1300 - 1358) was a French priest who sowed the seeds of religious scepticism in Europe. ... The Theory of impetus is a now obsolete theory of Classical mechanics developed in the 14th century. ...

Abū Rayhān al-Bīrūnī (973-1048) was the first physicist to realize that acceleration is connected with non-uniform motion.^[12] The first scientist to reject Aristotle's idea that a constant force produces uniform motion was the Arabic Muslim physicist and philosopher Hibat Allah Abu'l-Barakat al-Baghdaadi in the early 12th century. He was the first to argue that a force applied continuously produces acceleration, which is considered "the fundamental law of classical mechanics",^[13] and vaguely foreshadows Newton's second law of motion. (September 15, 973 in Kath, Khwarezm – December 13, 1048 in Ghazni) was a Persian[1][2][3] Muslim polymath[4] of the 11th century, whose experiments and discoveries were as significant and diverse as those of Leonardo da Vinci or Galileo, five hundred years before the Renaissance; al-Biruni was... Acceleration is the time rate of change of velocity and/or direction, and at any point on a velocity-time graph, it is given by the slope of the tangent to the curve at that point. ... Hibat Allah Abul-Barakat al-Baghdaadi (1080? - 1165?) was an Arab philosopher and physicist. ... Acceleration is the time rate of change of velocity and/or direction, and at any point on a velocity-time graph, it is given by the slope of the tangent to the curve at that point. ... Classical mechanics (commonly confused with Newtonian mechanics, which is a subfield thereof) is used for describing the motion of macroscopic objects, from projectiles to parts of machinery, as well as astronomical objects, such as spacecraft, planets, stars, and galaxies. ... Newtons laws of motion are the three scientific laws which Isaac Newton discovered concerning the behaviour of moving bodies. ...

In the early 16th century, al-Birjandi, in his analysis on the Earth's rotation, developed a hypothesis similar to Galileo's notion of "circular inertia",^[14] which he described in the following observational test: Abd al-Ali ibn Muhammad ibn al-Husayn al-Birjandi (d. ... An animation showing the rotation of the Earth. ... In the scientific method, an experiment (Latin: ex- periri, of (or from) trying) is a set of observations performed in the context of solving a particular problem or question, to retain or falsify a hypothesis or research concerning phenomena. ...

"The small or large rock will fall to the Earth along the path of a line that is perpendicular to the plane (sath) of the horizon; this is witnessed by experience (tajriba). And this perpendicular is away from the tangent point of the Earth’s sphere and the plane of the perceived (hissi) horizon. This point moves with the motion of the Earth and thus there will be no difference in place of fall of the two rocks."^[15]

Theory of impetus

Main article: Theory of impetus

See also: Conatus

In the 14th century, Jean Buridan rejected the notion that a motion-generating property, which he named impetus, dissipated spontaneously. Buridan's position was that a moving object would be arrested by the resistance of the air and the weight of the body which would oppose its impetus.^[16] Buridan also maintained that impetus increased with speed; thus, his initial idea of impetus was similar in many ways to the modern concept of momentum. Despite the obvious similarities to more modern ideas of inertia, Buridan saw his theory as only a modification to Aristotle's basic philosophy, maintaining many other peripatetic views, including the belief that there was still a fundamental difference between an object in motion and an object at rest. Buridan also maintained that impetus could be not only linear, but also circular in nature, causing objects (such as celestial bodies) to move in a circle. The Theory of impetus is a now obsolete theory of Classical mechanics developed in the 14th century. ... Marcus Tullius Cicero (106 BC – 43 BC) Conatus, (Latin: an exertion, effort; an impulse, inclination; an undertaking),[1] is a term used in philosophy to refer to a few different theories on psychology and metaphysics. ... Jean Buridan, in Latin Joannes Buridanus (1300 - 1358) was a French priest who sowed the seeds of religious scepticism in Europe. ... This article is about momentum in physics. ... Peripatetic means wandering. The Peripatetics were a school of philosophy in ancient Greece. ...

Buridan's thought was followed up by his pupil Albert of Saxony (1316-1390) and the Oxford Calculators, who performed various experiments that further undermined the classical, Aristotelian view. Their work in turn was elaborated by Nicole Oresme who pioneered the practice of demonstrating laws of motion in the form of graphs. Albert of Saxony (Albertus de Saxonia, c. ... The Oxford Calculators were a group of 14th-century thinkers, almost all associated with Merton College, Oxford, who took a strikingly logico-mathematical approach to philosophical problems. ... Portrait of Nicole Oresme: Miniature of Nicole Oresmes Traité de l’espere, Bibliothèque Nationale, Paris, France, fonds français 565, fol. ...

Shortly before Galileo's theory of inertia, Giambattista Benedetti modified the growing theory of impetus to involve linear motion alone: Giambattista (Gianbattista) Benedetti (1530–1590) was a Venetian mathematician who wrote La gnomonica. ...

"…[Any] portion of corporeal matter which moves by itself when an impetus has been impressed on it by any external motive force has a natural tendency to move on a rectilinear, not a curved, path."^[17]

Benedetti cites the motion of a rock in a sling as an example of the inherent linear motion of objects, forced into circular motion.

Classical inertia

The law of inertia states that it is the tendency of an object to resist a change in motion.The Aristotelian division of motion into mundane and celestial became increasingly problematic in the face of the conclusions of Nicolaus Copernicus in the 16th century, who argued that the earth (and everything on it) was in fact never "at rest", but was actually in constant motion around the sun.^[18] Galileo, in his further development of the Copernican model, recognized these problems with the then-accepted nature of motion and, at least partially as a result, included a restatement of Aristotle's description of motion in a void as a basic physical principle: Copernicus redirects here. ... Galileo can refer to: Galileo Galilei, astronomer, philosopher, and physicist (1564 - 1642) the Galileo spacecraft, a NASA space probe that visited Jupiter and its moons the Galileo positioning system Life of Galileo, a play by Bertolt Brecht Galileo (1975) - screen adaptation of the play Life of Galileo by Bertolt Brecht...

A body moving on a level surface will continue in the same direction at a constant speed unless disturbed.

It is also worth noting that Galileo later went on to conclude that based on this initial premise of inertia, it is impossible to tell the difference between a moving object and a stationary one without some outside reference to compare it against.^[19] This observation ultimately came to be the basis for Einstein to develop the theory of Special Relativity. Einstein redirects here. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ...

Galileo's concept of inertia would later come to be refined and codified by Isaac Newton as the first of his Laws of Motion (first published in Newton's work, Philosophiae Naturalis Principia Mathematica, in 1687): Sir Isaac Newton FRS (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... Newtons First and Second laws, in Latin, from the original 1687 edition of the Principia Mathematica. ... Newtons own copy of his Principia, with handwritten corrections for the second edition. ...

Unless acted upon by an unbalanced force, an object will maintain a constant velocity.

Note that "velocity" in this context is defined as a vector, thus Newton's "constant velocity" implies both constant speed and constant direction (and also includes the case of zero speed, or no motion). Since initial publication, Newton's Laws of Motion (and by extension this first law) have come to form the basis for the almost universally accepted branch of physics now termed classical mechanics. In physics and in vector calculus, a spatial vector is a concept characterized by a magnitude, which is a scalar, and a direction (which can be defined in a 3-dimensional space by the Euler angles). ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... Classical mechanics (commonly confused with Newtonian mechanics, which is a subfield thereof) is used for describing the motion of macroscopic objects, from projectiles to parts of machinery, as well as astronomical objects, such as spacecraft, planets, stars, and galaxies. ...

The actual term "inertia" was first introduced by Johannes Kepler in his Epitome Astronomiae Copernicanae (published in three parts from 1618-1621); however, the meaning of Kepler's term (which he derived from the Latin word for "idleness" or "laziness") was not quite the same as its modern interpretation. Kepler defined inertia only in terms of a resistance to movement, once again based on the presumption that rest was a natural state which did not need explanation. It was not until the later work of Galileo and Newton unified rest and motion in one principle that the term "inertia" could be applied to these concepts as it is today. Kepler redirects here. ...

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 actually 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 basically equivalent.

Relativity

Albert Einstein's theory of Special Relativity, as proposed in his 1905 paper, "On the Electrodynamics of Moving Bodies," was built on the understanding of inertia and inertial reference frames developed by Galileo and Newton. While this revolutionary theory did significantly change the meaning of many Newtonian concepts such as mass, energy, and distance, Einstein's concept of inertia remained unchanged from Newton's original meaning (in fact the entire theory was based on Newton's definition of inertia). However, this resulted in a limitation inherent in Special Relativity that it could only apply when reference frames were inertial in nature (meaning when no acceleration was present). In an attempt to address this limitation, Einstein proceeded to develop his theory of General Relativity ("The Foundation of the General Theory of Relativity," 1916), which ultimately provided a unified theory for both inertial and noninertial (accelerated) reference frames. However, in order to accomplish this, in General Relativity Einstein found it necessary to redefine several fundamental aspects of the universe (such as gravity) in terms of a new concept of "curvature" of spacetime, instead of the more traditional system of forces understood by Newton. “Einstein” redirects here. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... In physics, an inertial frame of reference, or inertial frame for short (also descibed as absolute frame of reference), is a frame of reference in which the observers move without the influence of any accelerating or decelerating force. ... For other uses, see Mass (disambiguation). ... Distance is a numerical description of how far apart objects are at any given moment in time. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... For other uses of this term, see Spacetime (disambiguation). ...

As a result of this redefinition, Einstein also redefined the concept of "inertia" in terms of geodesic deviation instead, with some subtle but significant additional implications. The result of this is that according to General Relativity, when dealing with very large scales, the traditional Newtonian idea of "inertia" does not actually apply, and cannot necessarily be relied upon. Luckily, for sufficiently small regions of spacetime, the Special Theory can still be used, in which inertia still means the same (and works the same) as in the classical model. Towards the end of his life it seems as if Einstein had become convinced that space-time is a new form of aether, in some way serving as a reference frame for the property of inertia^[20] (Kostro, 2000). In differential geometry, the geodesic deviation equation is an equation involving the Riemann curvature tensor, which measures the change in separation of neighbouring geodesics. ... The luminiferous aether: it was hypothesised that the Earth moves through a medium of aether that carries light In the late 19th century luminiferous aether (light-bearing aether) was the term used to describe a medium for the propagation of light. ...

Another profound, perhaps the most well-known, conclusion of the theory of Special Relativity was that energy and mass are not separate things, but are, in fact, interchangeable. This new relationship, however, also carried with it new implications for the concept of inertia. The logical conclusion of Special Relativity was that if mass exhibits the principle of inertia, then inertia must also apply to energy as well. This theory, and subsequent experiments confirming some of its conclusions, have also served to radically expand the definition of inertia in some contexts to apply to a much wider context including energy as well as matter. 8]

Interpretations

According to Isaac Asimov

According to Isaac Asimov in "Understanding Physics": "This tendency for motion (or for rest) to maintain itself steadily unless made to do otherwise by some interfering force can be viewed as a kind of "laziness," a kind of unwillingness to make a change. And indeed, Newton's first law of motion As Isaac Asimov goes on to explain, "Newton's laws of motion represent assumptions and definitions and are not subject to proof. In particular, the notion of 'inertia' is as much an assumption as Aristotle's notion of 'natural place.'...To be sure, the new relativistic view of the universe advanced by Einstein makes it plain that in some respects Newton's laws of motion are only approximations...At ordinary velocities and distance, however, the approximations are extremely good." Isaac Asimov (January 2?, 1920?[1] – April 6, 1992), pronounced , originally Исаак Озимов but now transcribed into Russian as Айзек Азимов [1], was a Russian-born American author and professor of biochemistry, a highly successful writer, best known for his works of science fiction and for his popular science books. ... Sir Isaac Newton FRS (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... Newtons laws of motion are three scientific laws which Isaac Newton discovered concerning the behaviour of moving bodies. ... Isaac Asimov (January 2?, 1920?[1] – April 6, 1992), pronounced , originally Исаак Озимов but now transcribed into Russian as Айзек Азимов [1], was a Russian-born American author and professor of biochemistry, a highly successful writer, best known for his works of science fiction and for his popular science books. ...

Mass and 'inertia'

Physics and mathematics appear to be less inclined to use the original concept of inertia as "a tendency to maintain momentum" and instead favor the mathematically useful definition of inertia as the measure of a body's resistance to changes in momentum or simply a body's inertial mass. A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... For other meanings of mathematics or uses of math and maths, see Mathematics (disambiguation) and Math (disambiguation). ...

This was clear in the beginning of the 20th century, when the theory of relativity was not yet created. Mass, m, denoted something like amount of substance or quantity of matter. And at the same time mass was the quantitative measure of inertia of a body. Two-dimensional analogy of space-time curvature described in General Relativity. ...

The mass of a body determines the momentum P of the body at given velocity v; it is a proportionality factor in the formula:

P = mv

The factor m is referred to as inertial mass. Inertial mass is a measure of the resistance of an entity to a change in its velocity relative to an inertial frame. ...

But mass as related to 'inertia' of a body can be defined also by the formula:

F = ma

By this formula, the greater its mass, the less a body accelerates under given force. Masses m defined by the formula (1) and (2) are equal because the formula (2) is a consequence of the formula (1) if mass does not depend on time and speed. Thus, "mass is the quantitative or numerical measure of body’s inertia, that is of its resistance to being accelerated".

This meaning of a body's inertia therefore is altered from the original meaning as "a tendency to maintain momentum" to a description of the measure of how difficult it is to change the momentum of a body.

Inertial mass

The only difference there appears to be between inertial mass and gravitational mass is the method used to determine them.

Gravitational mass is measured by comparing the force of gravity of an unknown mass to the force of gravity of a known mass. This is typically done with some sort of balance scale. The beauty of this method is that no matter where, or on what planet you are, the masses will always balance out because the gravitational acceleration on each object will be the same. This does break down near supermassive objects such as black holes and neutron stars due to the high gradient of the gravitational field around such objects. Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... Gravity is a force of attraction that acts between bodies that have mass. ...

Inertial mass is found by applying a known force to an unknown mass, measuring the acceleration, and applying Newton's Second Law, m = F/a. This gives an accurate value for mass, limited only by the accuracy of the measurements. When astronauts need to be weighed in outer space, they actually find their inertial mass in a special chair.

The interesting thing is that, physically, no difference has been found between gravitational and inertial mass. Many experiments have been performed to check the values and the experiments always agree to within the margin of error for the experiment. Einstein used the fact that gravitational and inertial mass were equal to begin his Theory of General Relativity in which he postulated that gravitational mass was the same as inertial mass, and that the acceleration of gravity is a result of a 'valley' or slope in the space-time continuum that masses 'fell down' much as pennies spiral around a hole in the common donation toy at a chain store. Einstein redirects here. ... General relativity (GR) or general relativity theory (GRT) is the theory of gravitation published by Albert Einstein in 1915. ... In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional pseudo-Riemannian manifold called spacetime. ...

Since Einstein used inertial mass to describe Special Relativity, inertial mass is closely related to relativistic mass and is therefore different from rest mass. For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... The term mass in special relativity can be used in different ways, occasionally leading to confusion. ... The term mass in special relativity is used in a couple of different ways, occasionally leading to a great deal of confusion. ...

Inertial frames

In a location such as a steadily moving railway carriage, a dropped ball (as seen by an observer in the carriage) would behave as it would if it were dropped in a stationary carriage. The ball would simply descend vertically. It is possible to ignore the motion of the carriage by defining it as an inertial frame. In a moving but non-accelerating frame, the ball behaves normally because the train and its contents continue to move at a constant velocity. Before being dropped, the ball was traveling with the train at the same speed, and the ball's inertia ensured that it continued to move in the same speed and direction as the train, even while dropping. Note that, here, it is inertia which ensured that, not its mass. In physics, an inertial frame of reference, or inertial frame for short (also descibed as absolute frame of reference), is a frame of reference in which the observers move without the influence of any accelerating or decelerating force. ...

In an inertial frame all the observers in uniform (non-accelerating) motion will observe the same laws of physics. However observers in another inertial frame can make a simple, and intuitively obvious, transformation (the Galilean transformation), to convert their observations. Thus, an observer from outside the moving train could deduce that the dropped ball within the carriage fell vertically downwards. In physics, an inertial frame of reference, or inertial frame for short (also descibed as absolute frame of reference), is a frame of reference in which the observers move without the influence of any accelerating or decelerating force. ... The Galilean transformation is used to transform between the coordinates of two reference frames which differ only by constant relative motion within the constructs of Newtonian physics. ...

However, in frames which are experiencing acceleration (non-inertial frames), objects appear to be affected by fictitious forces. For example, if the railway carriage was accelerating, the ball would not fall vertically within the carriage but would appear to an observer to be deflected because the carriage and the ball would not be traveling at the same speed while the ball was falling. Other examples of fictitious forces occur in rotating frames such as the earth. For example, a missile at the North Pole could be aimed directly at a location and fired southwards. An observer would see it apparently deflected away from its target by a force (the Coriolis force) but in reality the southerly target has moved because earth has rotated while the missile is in flight. Because the earth is rotating, a useful inertial frame of reference is defined by the stars, which only move imperceptibly during most observations. A fictitious force is an apparent force that acts on all masses in a non-inertial frame of reference, e. ... In the inertial frame of reference (upper part of the picture), the black object moves in a straight line. ...

In summary, the principle of inertia is intimately linked with the principles of conservation of energy and conservation of momentum. Look up conservation of energy in Wiktionary, the free dictionary. ... This article is about momentum in physics. ...

Rotational inertia

Another form of inertia is rotational inertia (→ moment of inertia), which refers to the fact that a rotating rigid body maintains its state of uniform rotational motion. Its angular momentum is unchanged, unless an external torque is applied; this is also called conservation of angular momentum. Rotational inertia often has hidden practical consequences. Moment of inertia, also called mass moment of inertia and, sometimes, the angular mass, (SI units kg m2, Former British units slug ft2), is the rotational analog of mass. ... This article is about rotation as a movement of a physical body. ... This gyroscope remains upright while spinning due to its angular momentum. ... For other senses of this word, see torque (disambiguation). ...

See also

Inertia is a way to measure female behavior in life instances. For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... An inertial guidance system consists of an Inertial Measurement Unit (IMU) combined with a set of guidance algorithms and control mechanisms, allowing the path of a vehicle to be controlled according to the position determined by the inertial navigation system. ... The following is a list of moments of inertia. ... In theoretical physics, particularly in discussions of gravitation theories, Machs principle is the name given by Einstein to a vague hypothesis first supported by the physicist and philosopher Ernst Mach. ... Newtons First and Second laws, in Latin, from the original 1687 edition of the Principia Mathematica. ... Classical mechanics is a model of the physics of forces acting upon bodies. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... The cars of a roller coaster reach their maximum kinetic energy when at the bottom of their path. ...

Notes

The MacTutor history of mathematics archive is a website hosted by University of St Andrews in Scotland. ... The Dictionary of Scientific Biography is a reference work consisting of extensive biographies of scientists from antiquity to modern times, excluding scientists who were alive when the Dictionary was first put out. ... Look up Cf. ... Frontispiece and title page of the Dialogue The Dialogue Concerning the Two Chief World Systems (Dialogo sopra i due massimi sistemi del mondo) was a 1632 book by Galileo, comparing the Copernican system, and the traditional Ptolemaic system. ...

References

• Ragep, F. Jamil (2001a), "Tusi and Copernicus: The Earth's Motion in Context", Science in Context (Cambridge University Press) 14 (1-2): 145–163
• Ragep, F. Jamil (2001b), "Freeing Astronomy from Philosophy: An Aspect of Islamic Influence on Science", Osiris, 2nd Series 16 (Science in Theistic Contexts: Cognitive Dimensions): 49-64 & 66-71

The headquarters of the Cambridge University Press, in Trumpington Street, Cambridge. ...

External links

• Inertia (animation)
• Jean Buridan Stanford Encyclopaedia of Philosophy
• Inertia Formula

Books and papers

• Butterfield, H (1957) The Origins of Modern Science ISBN 0-7135-0160-X
• Clement, J (1982) "Students' preconceptions in introductory mechanics", American Journal of Physics vol 50, pp66-71
• Crombie, A C (1959) Medieval and Early Modern Science, vol 2
• McCloskey, M (1983) "Intuitive physics", Scientific American, April, pp114-123
• McCloskey, M & Carmazza, A (1980) "Curvilinear motion in the absence of external forces: naïve beliefs about the motion of objects", Science vol 210, pp1139-1141
• Masreliez, C.J., Motion, Inertia and Special Relativity – a Novel Perspective, Physica Scripta, (dec 2006)