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'''Gravitation''' is a [[phenomenon]] which attracts all objects within the [[universe]] to each other <ref>New Oxford American Dictionary, 2nd Edition</ref>. In modern [[physics]], it is explained by the [[Theory of relativity|General Theory of relativity]]. Before general relativity, gravitation was described by [[Sir Isaac Newton|Isaac Newton's]] law of universal gravitation, which is still useful in most situations.

'''Gravitation''' is a [[phenomenon]] which attracts all objects within the [[universe]] to each other <ref>New Oxford American Dictionary, 2nd Edition</ref>. In modern [[physics]], it is explained by the [[Theory of relativity|General Theory of relativity]]. Before general relativity, gravitation was described by [[Sir Isaac Newton|Isaac Newton's]] law of universal gravitation in his [[Philosophiæ Naturalis Principia Mathematica|''Principia Mathematica'']], which is still useful in most situations.

Everything in the universe that has mass attracts every other thing that has mass. How much depends on the size of the masses 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 the scales. 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.

Everything in the universe that has mass attracts every other thing that has mass. How much depends on the size of the masses 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 the scales. 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 is stated as

The law itself states that each particle in the universe attracts another particle with a force directly [[proportion|proportional]] 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>

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

Where the force due to gravity equals the mass of the first object, ''m''₁, is multiplied by the mass of the second object, ''m''₂, which is then divided by the distace between the center of mass of both objects, r, squared. This is then multipled by the [[gravitational constant]]: 6.67428x10^-11 N m² Kg ^-2

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.

 

''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]].

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]].

==Gravity and Modern Physics==

==Gravity and Modern Physics==

Newton's [[Theory of Gravity]] was one of the earliest triumphs of modern [[physics]]. It now stands as both one of the most successful and most mysterious areas of that field. 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.

Newton's [[Theory of Gravity]] was one of the earliest triumphs of modern [[physics]]. It now stands as both one of the most successful and most mysterious areas of that field. 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]] 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.

== References ==

== References ==