## ::Newton's laws of motion

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Newton's First and Second laws, in Latin, from the original 1687 Principia Mathematica.

Newton's laws of motion are three physical laws that, together, laid the foundation for classical mechanics. They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces. They have been expressed in several different ways, over nearly three centuries,<ref>For explanations of Newton's laws of motion by Newton in the early 18th century, by the physicist William Thomson (Lord Kelvin) in the mid-19th century, and by a modern text of the early 21st century, see:-

 First law: When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force.{{#invoke:citation/CS1|citation CitationClass=book }}{{#invoke:citation/CS1|citation CitationClass=book }} Second law: The vector sum of the external forces F on an object is equal to the mass m of that object multiplied by the acceleration vector a of the object: F = ma. Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

The three laws of motion were first compiled by Isaac Newton in his Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), first published in 1687.<ref name=Principia>See the Principia on line at Andrew Motte Translation</ref> Newton used them to explain and investigate the motion of many physical objects and systems.<ref name=Motte>Andrew Motte translation of Newton's Principia (1687) Axioms or Laws of Motion</ref> For example, in the third volume of the text, Newton showed that these laws of motion, combined with his law of universal gravitation, explained Kepler's laws of planetary motion.

Newton's laws of motion sections
Intro  Overview  Newton's first law  Newton's third law  History  Importance and range of validity  Relationship to the conservation laws  See also  References and notes  Further reading and works cited  External links

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