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Created page with 'File:lighterstill.jpg '''Inertia''' is the resistance of any physical object to a change in its state of relative motion. It is represented numerically b...'
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'''Inertia''' is the [[resistance]] of any [[physical]] object to a [[change]] in its state of [[relative]] [[motion]]. It is represented numerically by an object's [[mass]]. 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]]. Inertia comes from the [[Latin]] word, "iners", meaning idle, or lazy. Sir [[Isaac Newton]] defined inertia in Definition 3 of his Philosophiæ Naturalis Principia Mathematica, which states:[1]

*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 [[Status quo|present state]], whether it be of rest, or of moving [[uniformly]] forward in a straight 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), or sometimes to its [[momentum]], depending on the [[context]] (e.g. "this object has a lot of inertia"). The term "inertia" is more properly understood as shorthand for "the principle of inertia" as described by Newton in his ''[http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion First Law of Motion]''. This [[law]], [[expressed]] simply, says that an object that is not subject to any net external force moves at a constant velocity. In even simpler terms, inertia means that an object will always continue moving at its current speed and in its current direction until some force causes its speed or direction to [[change]]. This would include an object that is not in motion (velocity = zero), which will remain at rest until some force causes it to move.

On the surface of the Earth the nature of inertia is often masked by the effects of [[friction]], which generally tends to decrease the speed of moving objects (often even to the point of rest), and by the acceleration due to [[gravity]]. The effects of these two forces misled [[classical]] [[theorists]] such as [http://en.wikipedia.org/wiki/Aristotle Aristotle], who believed that objects would move only as long as force was being applied to them.[2][http://en.wikipedia.org/wiki/Inertia]
==Notes==
# Isaac Newton, Mathematical Principles of Natural Philosophy translated into English by Andrew Motte, First American Edition, New York, 1846, page 72.
# Pages 2 to 4, Section 1.1, "Skating", Chapter 1, "Things that Move", Louis Bloomfield, Professor of Physics at the University of Virginia, How Everything Works: Making Physics Out of the Ordinary, John Wiley & Sons (2007), hardcover, 720 pages, ISBN 978-0-471-74817-5
# Aristotle, Physics, 8.10, 267a1-21; Aristotle, Physics, trans. by R. P. Hardie and R. K. Gaye.
==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
==External links==
*[http://www.bigs.de/BLH/en/index.php?option=com_content&view=category&layout=blog&id=78&Itemid=246 BIGS - Lernhilfe für Physik und Technik]
*[http://www.seop.leeds.ac.uk/entries/buridan/ ''Jean Buridan'' Stanford Encyclopaedia of Philosophy]
*[http://www.geom.uiuc.edu/education/calc-init/static-beam/mnt-derive.html 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, pp 66–71
* Crombie, A C (1959) Medieval and Early Modern Science, vol 2
* McCloskey, M (1983) "Intuitive physics", Scientific American, April, pp 114–123
* 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)

[[Category: Physics]]