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[[Image:lighterstill.jpg]][[Image:Gforce.jpg|right|frame]]
 
[[Image:lighterstill.jpg]][[Image:Gforce.jpg|right|frame]]
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In [[physics]], '''force''' is anything that can cause a [[mass]] to accelerate. It may be experienced as a lift, a push, or a pull. The acceleration of the body is proportional to the [[vector sum]] of all forces acting on it (known as ''net force'' or ''resultant force''). In an extended body, force may also cause rotation, deformation, or an increase in pressure for the body. Rotational effects are determined by the torques, while deformation and pressure are determined by the [[stress]]es that the forces create.  
 
In [[physics]], '''force''' is anything that can cause a [[mass]] to accelerate. It may be experienced as a lift, a push, or a pull. The acceleration of the body is proportional to the [[vector sum]] of all forces acting on it (known as ''net force'' or ''resultant force''). In an extended body, force may also cause rotation, deformation, or an increase in pressure for the body. Rotational effects are determined by the torques, while deformation and pressure are determined by the [[stress]]es that the forces create.  
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Although there are apparently many types of forces in the Universe, they are all based on four fundamental forces. The strong and weak forces only act at very short distances and are responsible for holding certain [[nucleons]] and compound nuclei  together. The electromagnetic force acts between [[electric charge]]s and the gravitational force acts between [[mass]]es. The [[Pauli exclusion principle]] is responsible for the tendency of [[atom]]s not to overlap each other, and is thus responsible for the "stiffness" or "rigidity" of matter, but this also depends on the electromagnetic force which binds the constituents of every [[atom]].
 
Although there are apparently many types of forces in the Universe, they are all based on four fundamental forces. The strong and weak forces only act at very short distances and are responsible for holding certain [[nucleons]] and compound nuclei  together. The electromagnetic force acts between [[electric charge]]s and the gravitational force acts between [[mass]]es. The [[Pauli exclusion principle]] is responsible for the tendency of [[atom]]s not to overlap each other, and is thus responsible for the "stiffness" or "rigidity" of matter, but this also depends on the electromagnetic force which binds the constituents of every [[atom]].
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All other forces are based on these four. For example, [[friction]] is a manifestation of the [[electromagnetic]] force acting between the [[atom]]s of two surfaces, and the Pauli exclusion principle, which does not allow atoms to pass through each other. The forces in springs modeled by [[Hooke's law]] are also the result of electromagnetic forces and the exclusion principle acting together to return the object to its equilibrium position. [[Centrifugal force]]s are acceleration forces which arise simply from the acceleration of rotating [[frames of reference]].
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All other forces are based on these four. For example, [[friction]] is a manifestation of the [[electromagnetic]] force acting between the [[atom]]s of two surfaces, and the Pauli exclusion principle, which does not allow atoms to pass through each other. The forces in springs modeled by [[Hooke's law]] are also the result of electromagnetic forces and the exclusion principle acting together to return the object to its equilibrium position. [[Centrifugal force]]s are acceleration forces which arise simply from the acceleration of rotating [[Frame of reference|frames of reference]].
    
There is currently some debate to whether there are five forces not four. The discovery of dark energy which acts on an even larger scale than [[gravity]] (with an opposing effect) and is a unique and separate force.  
 
There is currently some debate to whether there are five forces not four. The discovery of dark energy which acts on an even larger scale than [[gravity]] (with an opposing effect) and is a unique and separate force.  
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As well as being added, forces can also be broken down (or 'resolved'). For example, a horizontal force pointing northeast can be split into two forces, one pointing north, and one pointing east. Summing these component forces using vector addition yields the original force.  Force vectors can also be three-dimensional, with the third (vertical) component at right-angles to the two horizontal components.
 
As well as being added, forces can also be broken down (or 'resolved'). For example, a horizontal force pointing northeast can be split into two forces, one pointing north, and one pointing east. Summing these component forces using vector addition yields the original force.  Force vectors can also be three-dimensional, with the third (vertical) component at right-angles to the two horizontal components.
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The simplest case of static equilibrium is when two forces are equal in magnitude but opposite in direction.  This remains the most usual way of measuring forces, using simple devices such as weighing scales and spring balances. Using such tools, several quantitative force laws were discovered: that the force of gravity is proportional to volume for objects made of a given material (widely exploited for millennia to define standard weights); Archimedes' principle for bouyancy; [[Archimedes]]' analysis of the [[lever]]; [[Boyle's law]] for gas pressure; and [[Hooke's law]] for springs: all these were all formulated and experimentally verified before [[Isaac Newton]] expounded his three laws of motion.[http://en.wikipedia.org/wiki/Force]
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The simplest case of static equilibrium is when two forces are equal in magnitude but opposite in direction.  This remains the most usual way of measuring forces, using simple devices such as weighing scales and spring balances. Using such tools, several quantitative force laws were discovered: that the force of gravity is proportional to volume for objects made of a given material (widely exploited for millennia to define standard weights); Archimedes' principle for bouyancy; [[Archimedes]]' analysis of the [[lever]]; [[Boyle's law]] for gas pressure; and [[Hooke's law]] for springs: all these were all formulated and experimentally verified before [[Isaac Newton]] expounded his three laws of motion.[https://en.wikipedia.org/wiki/Force]
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==References==
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# "glossary". Earth Observatory. NASA. Retrieved on 2008-04-09. "Force: Any external agent that causes a change in the motion of a free body, or that causes stress in a fixed body."
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# See for example pages 9-1 and 9-2 of Feynman, Leighton and Sands (1963).
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# Feynman, R. P., Leighton, R. B., Sands, M. (1963). Lectures on Physics, Vol 1. Addison-Wesley. ; Kleppner, D., Kolenkow, R. J. (1973). An introduction to mechanics. McGraw-Hill. .
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# University Physics, Sears, Young & Zemansky, pp18–38
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# Heath,T.L.. "The Works of Archimedes (1897). The unabridged work in PDF form (19 MB)". Archive.org. Retrieved on 2007-10-14.
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# Weinberg, S. (1994). Dreams of a Final Theory. Vintage Books USA. ISBN 0-679-74408-8
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# Land, Helen The Order of Nature in Aristotle's Physics: Place and the Elements (1998)
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# Hetherington, Norriss S. (1993). Cosmology: Historical, Literary, Philosophical, Religious, and Scientific Perspectives. Garland Reference Library of the Humanities. p. 100. ISBN 0815310854.
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# Drake, Stillman (1978). Galileo At Work. Chicago: University of Chicago Press. ISBN 0-226-16226-5
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# Newton, Isaac (1999). The Principia Mathematical Principles of Natural Philosophy. Berkeley: University of California Press. ISBN 0-520-08817-4.  This is a recent translation into English by I. Bernard Cohen and Anne Whitman, with help from Julia Budenz.
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# DiSalle, Robert (2002-03-30). "Space and Time: Inertial Frames". Stanford Encyclopedia of Philosophy. Retrieved on 2008-03-24.
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# Newton's Principia Mathematica actually used a finite difference version of this equation based upon impulse. See Impulse.
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# Halliday; Resnick. Physics. 1. pp. 199. "It is important to note that we cannot derive a general expression for Newton's second law for variable mass systems by treating the mass in F = dP/dt = d(Mv) as a variable. [...] We can use F = dP/dt to analyze variable mass systems only if we apply it to an entire system of constant mass having parts among which there is an interchange of mass."  [Emphasis as in the original]
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# Kleppner; Kolenkow. An Introduction to Mechanics. pp. 133–134. "Recall that F = dP/dt was established for a system composed of a certain set of particles...it is essential to deal with the same set of particles throughout the time interval...Consequently, the mass of the system can not change during the time of interest."
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# For example, by Rob Knop PhD in his Galactic Interactions blog on February 26, 2007 at 9:29 a.m. [1]
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# One exception to this rule is: Landau, L. D.; Akhiezer, A. I.; Lifshitz, A. M. (1967). General Physics; mechanics and molecular physics (First English ed.). Oxford: Pergamon Press.  Translated by: J. B. Sykes, A. D. Petford, and C. L. Petford. Library of Congress Catalog Number 67-30260. In section 7, pages 12–14, this book defines force as dp/dt.
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# e.g. W. Noll, “On the Concept of Force”, in part B of Walter Noll's website..
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# Henderson, Tom (1996-2007). "Lesson 4: Newton's Third Law of Motion". The Physics Classroom. Retrieved on 2008-01-04.
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# Dr. Nikitin (2007). "Dynamics of translational motion". Retrieved on 2008-01-04.
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#  "Introduction to Free Body Diagrams". Physics Tutorial Menu. University of Guelph. Retrieved on 2008-01-02.
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# Henderson, Tom (2004). "The Physics Classroom". The Physics Classroom and Mathsoft Engineering & Education, Inc.. Retrieved on 2008-01-02.
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# "Static Equilibrium". Physics Static Equilibrium (forces and torques). University of the Virgin Islands. Retrieved on 2008-01-02.
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# Shifman, Mikhail (1999). ITEP LECTURES ON PARTICLE PHYSICS AND FIELD THEORY. World Scientific. ISBN 981-02-2639-X.
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# Cutnell. Physics, Sixth Edition. pp. 855–876.
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# "Seminar: Visualizing Special Relativity". THE RELATIVISTIC RAYTRACER. Retrieved on 2008-01-04.
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# Wilson, John B.. "Four-Vectors (4-Vectors) of Special Relativity: A Study of Elegant Physica". The Science Realm: John's Virtual Sci-Tech Universe. Retrieved on 2008-01-04.
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# Nave, R. "Pauli Exclusion Principle". HyperPhysics***** Quantum Physics. Retrieved on 2008-01-02.
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# "Fermions & Bosons". The Particle Adventure. Retrieved on 2008-01-04.
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# Cook, A. H. (16-160-1965). "A New Absolute Determination of the Acceleration due to Gravity at the National Physical Laboratory". Nature 208: 279. doi:10.1038/208279a0. https://www.nature.com/nature/journal/v208/n5007/abs/208279a0.html. Retrieved on 4 January 2008.
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# University Physics, Sears, Young & Zemansky, pp59–82
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# "Sir Isaac Newton: The Universal Law of Gravitation". Astronomy 161 The Solar System. Retrieved on 2008-01-04.
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# Watkins, Thayer. "Perturbation Analysis, Regular and Singular". Department of Economics. San José State University.
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# Kollerstrom, Nick (2001). "Neptune's Discovery. The British Case for Co-Prediction.". University College London. Archived from the original on 2005-11-11. Retrieved on 2007-03-19.
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# Einstein, Albert (1916). "The Foundation of the General Theory of Relativity" (PDF). Annalen der Physik 49: 769–822. https://www.alberteinstein.info/gallery/gtext3.html. Retrieved on 3 September 2006.
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# Cutnell. Physics, Sixth Edition. p. 519.
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# Coulomb, Charles (1784). "Recherches théoriques et expérimentales sur la force de torsion et sur l'élasticité des fils de metal". Histoire de l’Académie Royale des Sciences: 229–269.
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# Feynman, Leighton and Sands (2006). The Feynman Lectures on Physics The Definitive Edition Volume II. Pearson Addison Wesley. ISBN 0-8053-9047-2.
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# Duffin, William (1980). Electricity and Magnetism, 3rd Ed.. McGraw-Hill. pp. 364–383. ISBN 0-07-084111-X.
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# For a complete library on quantum mechanics see Quantum_mechanics#References
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# Cutnell. Physics, Sixth Edition. p. 940.
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# Cutnell. Physics, Sixth Edition. p. 951.
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# Stevens, Tab (10/07/2003). "Quantum-Chromodynamics: A Definition - Science Articles". Retrieved on 2008-01-04.
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# Cutnell. Physics, Sixth Edition. p. 93.
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# "Tension Force". Non-Calculus Based Physics I. Retrieved on 2008-01-04.
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# Fitzpatrick, Richard (2006-02-02). "Strings, pulleys, and inclines". Retrieved on 2008-01-04.
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# "Elasticity, Periodic Motion". HyperPhysics. Georgia State University. Retrieved on 2008-01-04.
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# Nave, R. "Centripetal Force". HyperPhysics***** Mechanics ***** Rotation.
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# Mallette, Vincent (1982-2008). "Inwit Publishing, Inc. and Inwit, LLC -- Writings, Links and Software Distributions - The Coriolis Force". Publications in Science and Mathematics, Computing and the Humanities. Inwit Publishing, Inc.. Retrieved on 2008-01-04.
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# "Newton's Second Law for Rotation". HyperPhysics***** Mechanics ***** Rotation. Retrieved on 2008-01-04.
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# Fitzpatrick, Richard (2007-01-07). "Newton's third law of motion". Retrieved on 2008-01-04.
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# Feynman, Leighton & Sands (1963), vol. 1, p. 13-3.
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# Feynman, Leighton & Sands (1963), vol. 1, p. 13-2.
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# Singh, Sunil Kumar (2007-08-25). "Conservative force". Connexions. Retrieved on 2008-01-04.
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# Davis, Doug. "Conservation of Energy". General physics. Retrieved on 2008-01-04.
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# Wandmacher, Cornelius; Johnson, Arnold (1995). Metric Units in Engineering. ASCE Publications. p. 15. ISBN 0784400709.
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# Corbell, H.C.; Philip Stehle (1994). Classical Mechanics p 28,. New York: Dover publications. ISBN 0-486-68063-0.
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# Cutnell, John d.; Johnson, Kenneth W. (2004). Physics, Sixth Edition. Hoboken, NJ: John Wiley & Sons Inc.. ISBN 041-44895-8.
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# Feynman, R. P., Leighton, R. B., Sands, M. (1963). Lectures on Physics, Vol 1. Addison-Wesley. ISBN 0-201-02116-1.
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# Halliday, David; Robert Resnick; Kenneth S. Krane (2001). Physics v. 1. New York: John Wiley & Sons. ISBN 0-471-32057-9.
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# Parker, Sybil (1993). Encyclopedia of Physics, p 443,. Ohio: McGraw-Hill. ISBN 0-07-051400-3.
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# Sears F., Zemansky M. & Young H. (1982). University Physics. Reading, MA: Addison-Wesley. ISBN 0-201-07199-1.
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# Serway, Raymond A. (2003). Physics for Scientists and Engineers. Philadelphia: Saunders College Publishing. ISBN 0-534-40842-7.
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# Tipler, Paul (2004). Physics for Scientists and Engineers: Mechanics, Oscillations and Waves, Thermodynamics (5th ed. ed.). W. H. Freeman. ISBN 0-7167-0809-4.
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# Verma, H.C. (2004). Concepts of Physics Vol 1. (2004 Reprint ed.). Bharti Bhavan. ISBN 81-7709-187-5.
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==Bibliography==
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# Corbell, H.C.; Philip Stehle (1994). Classical Mechanics p 28,. New York: Dover publications. ISBN 0-486-68063-0.
 +
# Cutnell, John d.; Johnson, Kenneth W. (2004). Physics, Sixth Edition. Hoboken, NJ: John Wiley & Sons Inc.. ISBN 041-44895-8.
 +
# Feynman, R. P., Leighton, R. B., Sands, M. (1963). Lectures on Physics, Vol 1. Addison-Wesley. ISBN 0-201-02116-1.
 +
# Halliday, David; Robert Resnick; Kenneth S. Krane (2001). Physics v. 1. New York: John Wiley & Sons. ISBN 0-471-32057-9.
 +
# Parker, Sybil (1993). Encyclopedia of Physics, p 443,. Ohio: McGraw-Hill. ISBN 0-07-051400-3.
 +
# Sears F., Zemansky M. & Young H. (1982). University Physics. Reading, MA: Addison-Wesley. ISBN 0-201-07199-1.
 +
# Serway, Raymond A. (2003). Physics for Scientists and Engineers. Philadelphia: Saunders College Publishing. ISBN 0-534-40842-7.
 +
# Tipler, Paul (2004). Physics for Scientists and Engineers: Mechanics, Oscillations and Waves, Thermodynamics (5th ed. ed.). W. H. Freeman. ISBN 0-7167-0809-4.
 +
# Verma, H.C. (2004). Concepts of Physics Vol 1. (2004 Reprint ed.). Bharti Bhavan. ISBN 81-7709-187-5.
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==External links==
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*[https://ocw.mit.edu/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/detail/Video-Segment-Index-for-L-6.htm Video lecture on Newton's three laws] by Walter Lewin from [https://ocw.mit.edu/ MIT OpenCourseWare]
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*[https://phy.hk/wiki/englishhtm/Vector.htm A Java simulation on vector addition of forces]
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*[https://www.lorenz-messtechnik.de/english/company/force_unit_calculation.php Force Unit Converter]
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[[Category: Physics]]
 
[[Category: Physics]]
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