Gravitation

2009-01-09T19:26:57Z

TimL:

'''The theory of Gravity''' is a [[Naturalism|naturalistic]] explanation for the mutual attraction of particles that contain mass. Before general relativity, gravitation was described by [[Sir Isaac Newton|Isaac Newton's]] naturalistic law of universal gravitation in his [[Philosophiæ Naturalis Principia Mathematica|''Principia Mathematica'']]. Issac Newton's current theory of gravity cannot explain the permutations of space and time as velocity of an object approaches the [[speed of light]]. [[Aristotle]], and other previous thinkers and scientists before Newton never proposed a mathematic explanation for attraction of masses. There is no direct evidence gravity actually exists, though some scientists identified with [[Big Science]] claim to identified gravity based on circumstantial evidence, such as apples falling from trees.

Everything in the universe that has mass attracts every other thing that has mass. The mechanism which transports this force has never been observed. Scientists have postulated the existence of a hypothetical particle, the [[graviton]], in order to uphold the naturalistic explanation absent of a supernatural force. The attraction depends on the mass of the objects and the distance between them. For normal objects, this pull is minute, but you can measure the pull between a very large object like the [[Earth]] and another object like you by standing on a scale. Your [[weight]] is the measure of the pull of gravity between you and the planet you are standing on. This [[force]] depends on your [[mass]] and the mass of that planet, but it also depends on your [[distance]] from the center of the planet. The further you are from the planet's center, the weaker the pull between it and your body. If you double your distance, the force is one quarter. At ten times the distance, the force is one hundredth. It drops off with the square of the distance. This is called the [[inverse square law]].<ref>http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html</ref>The force never becomes zero, no matter how far you travel.

The law itself states that each particle in the [[universe]] attracts another particle with a force directly [[proportion]]al to the product of their masses and inversely proportional to the [[exponentiation|square]] of the distance between them<ref>Serway and Beichner, Physics for Scientists and Engineers, Fifth Edition</ref>, or:

:<math>F = G \frac{m_1 m_2}{r^2}</math>

Where:

''F'' is the magnitude of the gravitational force.

''m''1 and ''m''2 are the object's masses.

''r'' is the distance that separates the objects' centers of mass.

''G'' is the [[gravitational constant]]: 6.67428x10-11 N m2 Kg -2

Gravitation is responsible for making objects accelerate towards each other as well as for the formation of the [[Earth]] and [[Sun]], the [[stars]] and the [[planets]].

An objects escape speed is the velocity required to escape the gravitational pull of a another object, usually a planet. It can be expressed as:

:<math>v = \sqrt \frac{2 G M}{R}</math>

Where:

''v'' is necessary velocity

''M'' is the mass of the planet

''R'' is the radius of the planet

''G'' is the [[gravitational constant]]: 6.67428x10-11 N m2 Kg -2

==Gravity and Modern Physics==
Newton's [[Theory of Gravity]] was one of the supposed earliest triumphs of modern [[physics]]. It now stands as both one of the most successful and most mysterious areas of that field. It is one of the few scientific theories that does not require a supernatural force to sustain self consistency. On one hand, the [[Theory_of_Relativity|General theory of Relativity]] is one of the most successful [[Scientific_Theory|scientific theories]] to date. On the other hand, how General Relativity might be reconciled with [[Quantum_mechanics|quantum physics]] during the first few milliseconds of the [[Big Bang]] remains an open question, and is one of the hotly contested areas among modern theoretical physicists. In the 1980s [[string theory]] was seen by many physicists as a more likely path towards a particular unification of gravity with the other fundamental forces (electromagnetism, the strong and weak nuclear forces), but the theory has been a failure.<ref>Not Even Wrong, Peter Woit [http://www.math.columbia.edu/~woit/wordpress/]</ref>

==See also==
*[[gravitational gradient]]

==External Links==
*[http://www.relativitycalculator.com/Newton_Universal_Gravity_Law.shtml   Newton's Universal Law of Gravitational Force]

== References ==
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[[category:physics]]

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Gravitation