Разлика помеѓу преработките на „Сила“

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{{Инфокутија физички единици мерки
{{Other uses|Force (disambiguation)|Forcing (disambiguation)}}
| bgcolor = green
| name = Сила
{{Infobox Physical quantity
| image = [[Податотека:Force examples.svg|200px]]
| name = Force
| caption = Силите се објаснуваат како поттурнување или повлекување на одредено тело. Оваа појава може да биде предеизвикана од [[гравитација]]та, [[магнетизам|магнетизмот]], или некое друго дејство кое може да предизвика забрзување.
| image = [[File:Force examples.svg|200px]]
| basequantities = 1 [[килограм|kg]]·[[метар|m]]/[[секунда|s]]<sup>2</sup>
| caption = Forces are also described as a push or pull on an object. They can be due to phenomena such as [[gravity]], [[magnetism]], or anything that might cause a mass to accelerate.
| unit = [[њутн (единица)|Њутн]]
| basequantities = 1 [[kilogram|kg]]·[[metre|m]]/[[second|s]]<sup>2</sup>
| unit = [[newton (unit)|newton]]
| symbols = ''F'', '''F'''
| derivations = '''F''' = ''[[масаMass|m]]'' [[забрзувањеAcceleration|'''a''']]
'''Силата''' ја создаваме со туркање или со потегнување. Силата дејствува врз определено тело на следните начини:
{{Classical mechanics|cTopic=Fundamental concepts}}
[[Податотека:Descomposicion de fuerzas en plano inclinado.png|мини|десно|300п|'''''']]
In [[physics]], a '''force''' is any interaction that, when unopposed, will change the [[motion (physics)|motion]] of an [[Physical body|object]].<ref>{{cite web|last1=Nave|first1=C. R.|title=Force|url=http://hyperphysics.phy-astr.gsu.edu/hbase/force.html|website=Hyperphysics|publisher=Dept. of Physics and Astronomy, Georgia State University|accessdate=15 August 2014|year=2014}}</ref> In other words, a force can cause an object with [[mass]] to change its [[velocity]] (which includes to begin moving from a [[Newton's first law|state of rest]]), i.e., to [[accelerate]]. Force can also be described by intuitive concepts such as a push or a pull. A force has both [[Euclidean vector#Length|magnitude]] and [[Direction (geometry, geography)|direction]], making it a [[Vector (geometric)|vector]] quantity. It is measured in the [[SI unit]] of [[newton (unit)|newtons]] and represented by the symbol '''F'''.
The original form of [[Newton's second law]] states that the net force acting upon an object is equal to the [[time derivative|rate]] at which its [[momentum]] changes with time. If the mass of the object is constant, this law implies that the [[acceleration]] of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the [[mass]] of the object
Related concepts to force include: [[thrust]], which increases the velocity of an object; [[Drag (physics)|drag]], which decreases the velocity of an object; and [[torque]], which produces [[angular acceleration|changes in rotational speed]] of an object. In an extended body, each part usually applies forces on the adjacent parts; the distribution of such forces through the body is the so-called [[stress (mechanics)|mechanical stress]]. [[Pressure]] is a simple type of stress. Stress usually causes [[deformation (engineering)|deformation]] of solid materials, or flow in [[fluid]]s.
==Development of the concept==
* силата може да го придвижи телото;
Philosophers in [[Classical antiquity|antiquity]] used the concept of force in the study of [[statics|stationary]] and [[dynamics (physics)|moving]] objects and [[simple machine]]s, but thinkers such as [[Aristotle]] and [[Archimedes]] retained fundamental errors in understanding force. In part this was due to an incomplete understanding of the sometimes non-obvious force of [[friction]], and a consequently inadequate view of the nature of natural motion.<ref name="Archimedes">{{cite web |last=Heath, T.L. |url=https://archive.org/details/worksofarchimede029517mbp |title=''The Works of Archimedes'' (1897). The unabridged work in PDF form (19&nbsp;MB) |publisher=[[Internet Archive]] |accessdate=2007-10-14}}</ref> A fundamental error was the belief that a force is required to maintain motion, even at a constant velocity. Most of the previous misunderstandings about motion and force were eventually corrected by [[Galileo Galilei]] and [[Sir Isaac Newton]]. With his mathematical insight, [[Sir Isaac Newton]] formulated [[Newton's laws of motion|laws of motion]] that were not improved-on for nearly three hundred years.<ref name=uniphysics_ch2/> By the early 20th century, [[Albert Einstein|Einstein]] developed a [[theory of relativity]] that correctly predicted the action of forces on objects with increasing momenta near the speed of light, and also provided insight into the forces produced by gravitation and [[inertia]].
With modern insights into [[quantum mechanics]] and technology that can accelerate particles close to the speed of light, [[particle physics]] has devised a [[Standard Model]] to describe forces between particles smaller than atoms. The [[Standard Model]] predicts that exchanged particles called [[gauge boson]]s are the fundamental means by which forces are emitted and absorbed. Only four main interactions are known: in order of decreasing strength, they are: [[strong force|strong]], [[electromagnetic force|electromagnetic]], [[weak force|weak]], and [[gravitational force|gravitational]].<ref name=FeynmanVol1>{{harvnb|Feynman volume 1}}</ref>{{rp|2–10}}<ref name=Kleppner />{{rp|79}} [[High energy physics|High-energy particle physics]] [[observation]]s made during the 1970s and 1980s confirmed that the weak and electromagnetic forces are expressions of a more fundamental [[electroweak]] interaction.<ref name="final theory"/>
* силата може да го забрза телото;
==Pre-Newtonian concepts==
* силата може да го забави телото;
{{see also|Aristotelian physics|Theory of impetus}}
[[File:Aristoteles Louvre2.jpg|thumb|right|[[Aristotle]] famously described a force as anything that causes an object to undergo "unnatural motion"]]
Since antiquity the concept of force has been recognized as integral to the functioning of each of the [[simple machine]]s. The [[mechanical advantage]] given by a simple machine allowed for less force to be used in exchange for that force acting over a greater distance for the same amount of [[work (physics)|work]]. Analysis of the characteristics of forces ultimately culminated in the work of [[Archimedes]] who was especially famous for formulating a treatment of [[buoyant force]]s inherent in [[fluid]]s.<ref name="Archimedes"/>
[[Aristotle]] provided a [[philosophical]] discussion of the concept of a force as an integral part of [[Physics (Aristotle)|Aristotelian cosmology]]. In Aristotle's view, the terrestrial sphere contained four [[Classical element|elements]] that come to rest at different "natural places" therein. Aristotle believed that motionless objects on Earth, those composed mostly of the elements earth and water, to be in their natural place on the ground and that they will stay that way if left alone. He distinguished between the innate tendency of objects to find their "natural place" (e.g., for heavy bodies to fall), which led to "natural motion", and unnatural or forced motion, which required continued application of a force.<ref>{{cite book|last=Lang|first=Helen S.|title=The order of nature in Aristotle's physics : place and the elements|year=1998|publisher=Cambridge Univ. Press|location=Cambridge|isbn=9780521624534|edition=1. publ.}}</ref> This theory, based on the everyday experience of how objects move, such as the constant application of a force needed to keep a cart moving, had conceptual trouble accounting for the behavior of [[projectile]]s, such as the flight of arrows. The place where the archer moves the projectile was at the start of the flight, and while the projectile sailed through the air, no discernible efficient cause acts on it. Aristotle was aware of this problem and proposed that the air displaced through the projectile's path carries the projectile to its target. This explanation demands a continuum like air for change of place in general.<ref name="Hetherington">{{cite book |first=Norriss S. |last=Hetherington |title=Cosmology: Historical, Literary, Philosophical, Religious, and Scientific Perspectives |page=100 |publisher= Garland Reference Library of the Humanities |year=1993 |isbn=0-8153-1085-4}}</ref>
* силата може да ја промени насоката на движење на телото;
[[Aristotelian physics]] began facing criticism in [[Science in the Middle Ages|Medieval science]], first by [[John Philoponus]] in the 6th century.
* силата може да го промени обликот на телото.
The shortcomings of Aristotelian physics would not be fully corrected until the 17th century work of [[Galileo Galilei]], who was influenced by the late Medieval idea that objects in forced motion carried an innate force of [[impetus theory|impetus]]. Galileo constructed an experiment in which stones and cannonballs were both rolled down an incline to disprove the [[Aristotelian theory of gravity|Aristotelian theory of motion]] early in the 17th century. He showed that the bodies were accelerated by gravity to an extent that was independent of their mass and argued that objects retain their [[velocity]] unless acted on by a force, for example [[friction]].<ref name="Galileo">Drake, Stillman (1978). Galileo At Work. Chicago: University of Chicago Press. ISBN 0-226-16226-5</ref>
Силата на привлекување меѓу телата се нарекува гравитација. Таа е една од најпознатите сили. Таа всушност не држи на земјата и ни дава тежина. Се што има маса - произведува гравитација, а таа сила зависи од масата на телата и нивната меѓусебна одалеченост. Колку едно тело е поразделечено од друго тело, толку привлечноста помеѓу нив ќе биде помала. [[месечина|Месечината]] на пример, привлекува со послаб интензитет од [[Земја|земјата]] затоа што има помала маса. За големата земјина маса, тежината на телата на неа се шест пати поголеми отколку што се на [[месечина|Месечината]].
==Newtonian mechanics==
Ако на едно тело делуваат повеќе сили, нивното дејство ќе биде како на него да делува една сила, но во средна насока. Таа сила се нарекува резултанта. Пример, кога две екипи влечат јаже, резултантата е скоро еднаква на нула затоа што приближно еднакви сили делуваат во спротивни насоки.
{{main|Newton's laws of motion}}
Sir Isaac Newton sought to describe the motion of all objects using the concepts of [[inertia]] and force, and in doing so he found that they obey certain [[conservation laws]]. In 1687, Newton went on to publish his thesis ''[[Philosophiæ Naturalis Principia Mathematica]]''.<ref name=uniphysics_ch2/><ref name="Principia">{{Cite book
|author-link= Isaac Newton
|title=The Principia Mathematical Principles of Natural Philosophy
|publisher=University of California Press |year=1999 |location=Berkeley
|isbn=0-520-08817-4}} This is a recent translation into English by I. Bernard Cohen and Anne Whitman, with help from Julia Budenz.</ref> In this work Newton set out three laws of motion that to this day are the way forces are described in physics.<ref name="Principia"/>
===First law===
Едно придвижено тело ќе продолжи да се движи во правец сè додека некоја сила не го скршне. За ѓулето да се врти во круг потребно е на него да се делува со сила која се нарекува центрипетална сила, која постојано го влече во средиштето на кругот. Штом атлетичарот ќе го испушти, ѓулето продолжува да се движи по права линија.
{{main|Newton's first law}}
Newton's First Law of Motion states that objects continue to move in a state of constant velocity unless acted upon by an external [[net force]] or ''resultant force''.<ref name="Principia"/> This law is an extension of Galileo's insight that constant velocity was associated with a lack of net force (see [[#Dynamic equilibrium|a more detailed description of this below]]). Newton proposed that every object with mass has an innate [[inertia]] that functions as the fundamental equilibrium "natural state" in place of the Aristotelian idea of the "natural state of rest". That is, the first law contradicts the intuitive Aristotelian belief that a net force is required to keep an object moving with constant velocity. By making ''rest'' physically indistinguishable from ''non-zero constant velocity'', Newton's First Law directly connects inertia with the concept of [[Galilean relativity|relative velocities]]. Specifically, in systems where objects are moving with different velocities, it is impossible to determine which object is "in motion" and which object is "at rest". In other words, to phrase matters more technically, the laws of physics are the same in every [[inertial frame of reference]], that is, in all frames related by a [[Galilean transformation]].
For instance, while traveling in a moving vehicle at a [[wikt:Constant|constant]] [[velocity]], the laws of physics do not change from being at rest. A person can throw a ball straight up in the air and catch it as it falls down without worrying about applying a force in the direction the vehicle is moving. This is true even though another person who is observing the moving vehicle pass by also observes the ball follow a curving [[parabola|parabolic path]] in the same direction as the motion of the vehicle. It is the inertia of the ball associated with its constant velocity in the direction of the vehicle's motion that ensures the ball continues to move forward even as it is thrown up and falls back down. From the perspective of the person in the car, the vehicle and everything inside of it is at rest: It is the outside world that is moving with a constant speed in the opposite direction. Since there is no experiment that can distinguish whether it is the vehicle that is at rest or the outside world that is at rest, the two situations are considered to be [[Galilean equivalence|physically indistinguishable]]. Inertia therefore applies equally well to constant velocity motion as it does to rest.
Притисокот е мерка за концентрација на силата. Силата применета на малечка површина создава многу поголем притисок од таа иста сила применета на голема површина. Доколку лопатката и кантата за полевање ги претиснеме со иста сила, лопатката во песокот ќе пропадне длабоко. Причината за тоа е во последниот случај силата се распоредува на помала површина, бидејќи лопатката има тенко сечило.
The concept of inertia can be further generalized to explain the tendency of objects to continue in many different forms of constant motion, even those that are not strictly constant velocity. The [[rotational inertia]] of planet Earth is what fixes the constancy of the length of a day and the length of a year. Albert Einstein extended the principle of inertia further when he explained that reference frames subject to constant acceleration, such as those free-falling toward a gravitating object, were physically equivalent to inertial reference frames. This is why, for example, astronauts experience [[weightlessness]] when in free-fall orbit around the Earth, and why Newton's Laws of Motion are more easily discernible in such environments. If an astronaut places an object with mass in mid-air next to himself, it will remain stationary with respect to the astronaut due to its inertia. This is the same thing that would occur if the astronaut and the object were in intergalactic space with no net force of gravity acting on their shared reference frame. This [[principle of equivalence]] was one of the foundational underpinnings for the development of the [[general theory of relativity]].<ref>{{cite web |first=Robert |last=DiSalle |url=http://plato.stanford.edu/entries/spacetime-iframes/ |accessdate=2008-03-24 |title=Space and Time: Inertial Frames |date=2002-03-30 |work=[[Stanford Encyclopedia of Philosophy]]}}</ref>
Единица за мерење на силата е Њутн. Еден њутн( 1N ) за една секунда забрзува тело од еден килограм за метар во секунда. Името на оваа мерна единица е ставено според англискиот математичар Исак Њутн, кој во 1687 година ги поставил трите закони кои го одредуваат движењето на телото под дејство на сила:
[[File:GodfreyKneller-IsaacNewton-1689.jpg|right|thumb|Though [[Sir Isaac Newton]]'s most famous equation is<br>
- '''телото не ја менува својата положба доколку на него не делува или влијае некоја друга сила;'''
<math>\scriptstyle{\vec{F}=m\vec{a}}</math>, he actually wrote down a different form for his second law of motion that did not use [[differential calculus]].]]
===Second law===
- '''телото го менува своето движење пропорционално на силата која дејствува на него, а обратнопропорционално на својата маса;'''
{{main|Newton's second law}}
A modern statement of Newton's Second Law is a vector equation:<ref group=Note>Newton's ''Principia Mathematica'' actually used a finite difference version of this equation based upon ''impulse''. See ''[[Newton's laws of motion#Impulse|Impulse]]''.</ref>
:<math>\vec{F} = \frac{\mathrm{d}\vec{p}}{\mathrm{d}t},</math>
where <math>\scriptstyle \vec{p}</math> is the [[momentum]] of the system, and <math>\scriptstyle \vec{F}</math> is the net ([[Vector (geometric)#Addition and subtraction|vector sum]]) force. In equilibrium, there is zero ''net'' force by definition, but (balanced) forces may be present nevertheless. In contrast, the second law states an ''unbalanced'' force acting on an object will result in the object's momentum changing over time.<ref name="Principia"/>
By the definition of [[Momentum#Linear momentum of a particle|momentum]],
:<math>\vec{F} = \frac{\mathrm{d}\vec{p}}{\mathrm{d}t} = \frac{\mathrm{d}\left(m\vec{v}\right)}{\mathrm{d}t},</math>
where ''m'' is the [[mass]] and <math>\scriptstyle \vec{v}</math> is the [[velocity]].<ref name=FeynmanVol1/>{{rp|9-1,9-2}}
Newton's second law applies only to a system of [[Newton's Laws of Motion#Open systems|constant mass]],<ref name=Halliday group=Note>"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''' = ''d'''''P'''/''dt'' = ''d''(''M'''''v''') as a ''variable''. [...] We ''can'' use '''F''' = ''d'''''P'''/''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] {{harv|Halliday|Resnick |Krane|2001|p=199}}</ref> and hence ''m'' may be moved outside the derivative operator. The equation then becomes
<math> F = {dp \over dt} = {{d(mv)} \over dt} = m {dv \over dt} = m.a </math>
:<math>\vec{F} = m\frac{\mathrm{d}\vec{v}}{\mathrm{d}t}.</math>
By substituting the definition of [[acceleration]], the algebraic version of [[Newton's Second Law]] is derived:
:<math>\vec{F} =m\vec{a}.</math>
Newton never explicitly stated the formula in the reduced form above.<ref>{{cite book|last=Howland|first=R. A.|title=Intermediate dynamics a linear algebraic approach|date=2006|publisher=Springer|location=New York|isbn=9780387280592|pages=255&ndash;256|edition=Online-Ausg.}}</ref>
Newton's Second Law asserts the direct proportionality of acceleration to force and the inverse proportionality of acceleration to mass. Accelerations can be defined through [[kinematic]] measurements. However, while kinematics are well-described through [[frame of reference|reference frame]] analysis in advanced physics, there are still deep questions that remain as to what is the proper definition of mass. [[General relativity]] offers an equivalence between [[space-time]] and mass, but lacking a coherent theory of [[quantum gravity]], it is unclear as to how or whether this connection is relevant on microscales. With some justification, Newton's second law can be taken as a quantitative definition of ''mass'' by writing the law as an equality; the relative units of force and mass then are fixed.
The use of Newton's Second Law as a ''definition'' of force has been disparaged in some of the more rigorous textbooks,<ref name=FeynmanVol1 />{{rp|12-1}}<ref name=Kleppner />{{rp|59}}<ref>One exception to this rule is: {{Cite book |last=Landau |first=L. D. |author-link=Lev Landau |last2=Akhiezer |author2-link=Aleksander Ilyich Akhiezer|first2=A. I. |last3=Lifshitz |first3=A. M. |author3-link=Evgeny Lifshitz |title=General Physics; mechanics and molecular physics |publisher=Pergamon Press |year=196 |location=Oxford |edition=First English |isbn=0-08-003304-0}}
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''.</ref> because it is essentially a mathematical [[truism]]. Notable physicists, philosophers and mathematicians who have sought a more explicit definition of the concept of force include [[Ernst Mach]], [[Clifford Truesdell]]{{citation needed|date=October 2013}} and [[Walter Noll]].<ref>{{cite book|last=Jammer|first=Max|title=Concepts of force : a study in the foundations of dynamics|year=1999|publisher=Dover Publications|location=Mineola, N.Y.|isbn=9780486406893|pages=220–222|edition=Facsim.}}</ref><ref>{{cite web |first=Walter |last=Noll |title=On the Concept of Force |url=http://www.math.cmu.edu/~wn0g/Force.pdf |format=pdf |publisher=Carnegie Mellon University |date=April 2007 |accessdate=28 October 2013}}</ref>
Newton's Second Law can be used to measure the strength of forces. For instance, knowledge of the masses of [[planet]]s along with the accelerations of their [[orbit]]s allows scientists to calculate the gravitational forces on planets.
:''F'' е силата, измерeна во [[њутн (единица)|њутни]] (N),
===Third law===
:''t'' е времето, измерeно во [[секунда|секундии]] (s),
{{main|Newton's third law}}
Newton's Third Law is a result of applying [[symmetry]] to situations where forces can be attributed to the presence of different objects. The third law means that all forces are ''interactions'' between different bodies,<ref>{{cite journal
|title=Newton's third law revisited
|author=C. Hellingman
|journal=Phys. Educ.
|quote=Quoting Newton in the ''Principia'': It is not one action by which the Sun attracts Jupiter, and another by which Jupiter attracts the Sun; but it is one action by which the Sun and Jupiter mutually endeavour to come nearer together.
|doi=10.1088/0031-9120/27/2/011 |bibcode=1992PhyEd..27..112H}}</ref><ref group=Note>"Any single force is only one aspect of a mutual interaction between ''two'' bodies." {{harv|Halliday|Resnick |Krane|2001|pp=78–79}}</ref> and thus that there is no such thing as a unidirectional force or a force that acts on only one body. Whenever a first body exerts a force '''''F''''' on a second body, the second body exerts a force −'''''F''''' on the first body. '''''F''''' and −'''''F''''' are equal in magnitude and opposite in direction. This law is sometimes referred to as the ''[[Reaction (physics)|action-reaction law]]'', with '''''F''''' called the "action" and −'''''F''''' the "reaction". The action and the reaction are simultaneous:
If object 1 and object 2 are considered to be in the same system, then the net force on the system due to the interactions between objects 1 and 2 is zero since
:''p'' е импулсот (моменталната состојба, функција на времето)
This means that in a [[closed system]] of particles, there are no [[internal force]]s that are unbalanced. That is, the action-reaction force shared between any two objects in a closed system will not cause the [[center of mass]] of the system to accelerate. The constituent objects only accelerate with respect to each other, the system itself remains unaccelerated. Alternatively, if an [[external force]] acts on the system, then the center of mass will experience an acceleration proportional to the magnitude of the external force divided by the mass of the system.<ref name=FeynmanVol1 />{{rp|19-1}}<ref name=Kleppner />
:''v'' е брзината, измерeна во [[метар|метри]] во секунда (м/с или m/s),
Combining Newton's Second and Third Laws, it is possible to show that the [[Conservation of momentum|linear momentum of a system is conserved]]. Using
:''m'' е [[маса]]та, измерена во [[килограм]]и (кг или kg),
:<math>\vec{F}_{1,2} = \frac{\mathrm{d}\vec{p}_{1,2}}{\mathrm{d}t} = -\vec{F}_{2,1} = -\frac{\mathrm{d}\vec{p}_{2,1}}{\mathrm{d}t}</math>
:''a'' = <math>dv \over dt</math> е брзината, измерена во метри во секунда на квадрат (<math>m \over s^2</math>).
and [[integral|integrating]] with respect to time, the equation:
:<math>\Delta{\vec{p}_{1,2}} = - \Delta{\vec{p}_{2,1}}</math>
is obtained. For a system that includes objects 1 and 2,
- '''сите сили се појавуваат во парови. Силите се еднакви по големина но со спротивна насока;'''
:<math>\sum{\Delta{\vec{p}}}=\Delta{\vec{p}_{1,2}} + \Delta{\vec{p}_{2,1}} = 0</math>,
which is the conservation of linear momentum.<ref>{{cite web |last=Dr. Nikitin |title=Dynamics of translational motion |year=2007 |url=http://physics-help.info/physicsguide/mechanics/translational_dynamics.shtml |accessdate=2008-01-04}}</ref> Using the similar arguments, it is possible to generalize this to a system of an arbitrary number of particles. This shows that exchanging momentum between constituent objects will not affect the net momentum of a system. In general, as long as all forces are due to the interaction of objects with mass, it is possible to define a system such that net momentum is never lost nor gained.<ref name=FeynmanVol1 /><ref name=Kleppner />
Овие закони се наречени Њутнови закони за движењето на телата.
{{Нормативна контрола}}