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[[Image:lighterstill.jpg]][[Image:Gforce.jpg|right|frame]]
 
[[Image:lighterstill.jpg]][[Image:Gforce.jpg|right|frame]]
      
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]
 
==References==
 
==References==
 
# "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."
 
# "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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# Nave, R. "Pauli Exclusion Principle". HyperPhysics***** Quantum Physics. Retrieved on 2008-01-02.
 
# Nave, R. "Pauli Exclusion Principle". HyperPhysics***** Quantum Physics. Retrieved on 2008-01-02.
 
# "Fermions & Bosons". The Particle Adventure. Retrieved on 2008-01-04.
 
# "Fermions & Bosons". The Particle Adventure. Retrieved on 2008-01-04.
# 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. http://www.nature.com/nature/journal/v208/n5007/abs/208279a0.html. Retrieved on 4 January 2008.  
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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.  
 
# University Physics, Sears, Young & Zemansky, pp59–82
 
# University Physics, Sears, Young & Zemansky, pp59–82
 
# "Sir Isaac Newton: The Universal Law of Gravitation". Astronomy 161 The Solar System. Retrieved on 2008-01-04.
 
# "Sir Isaac Newton: The Universal Law of Gravitation". Astronomy 161 The Solar System. Retrieved on 2008-01-04.
 
# Watkins, Thayer. "Perturbation Analysis, Regular and Singular". Department of Economics. San José State University.
 
# Watkins, Thayer. "Perturbation Analysis, Regular and Singular". Department of Economics. San José State University.
 
# 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.
 
# 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.
# Einstein, Albert (1916). "The Foundation of the General Theory of Relativity" (PDF). Annalen der Physik 49: 769–822. http://www.alberteinstein.info/gallery/gtext3.html. Retrieved on 3 September 2006.  
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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.  
 
# Cutnell. Physics, Sixth Edition. p. 519.  
 
# Cutnell. Physics, Sixth Edition. p. 519.  
 
# 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.  
 
# 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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# Verma, H.C. (2004). Concepts of Physics Vol 1. (2004 Reprint ed.). Bharti Bhavan. ISBN 81-7709-187-5.
 
# Verma, H.C. (2004). Concepts of Physics Vol 1. (2004 Reprint ed.). Bharti Bhavan. ISBN 81-7709-187-5.
 
==External links==
 
==External links==
*[http://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 [http://ocw.mit.edu/ MIT OpenCourseWare]
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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]
*[http://phy.hk/wiki/englishhtm/Vector.htm A Java simulation on vector addition of forces]
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*[https://phy.hk/wiki/englishhtm/Vector.htm A Java simulation on vector addition of forces]
*[http://www.lorenz-messtechnik.de/english/company/force_unit_calculation.php Force Unit Converter]
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*[https://www.lorenz-messtechnik.de/english/company/force_unit_calculation.php Force Unit Converter]
       
[[Category: General Reference]]
 
[[Category: General Reference]]
 
[[Category: Physics]]
 
[[Category: Physics]]

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