View source for Physics:Dynamics (mechanics)

{{Short description|Branch of physics studying forces and their effect on motion}}
{{Classical mechanics}}

'''Dynamics''' is the branch of [[Physics:Classical mechanics|classical mechanics]] that is concerned with the study of [[Physics:Force|force]]s and their effects on [[Physics:Motion|motion]]. [[Biography:Isaac Newton|Isaac Newton]] was the first to formulate the fundamental [[Physical law|physical law]]s that govern dynamics in classical non-relativistic physics, especially his second law of motion.

==Principles==
Generally speaking, researchers involved in dynamics study how a physical system might develop or alter over time and study the causes of those changes.  In addition,  Newton established the fundamental physical laws which govern dynamics in physics. By studying his system of mechanics, dynamics can be understood. In particular, dynamics is mostly related to Newton's second law of motion. However, all three laws of motion are taken into account because these are interrelated in any given observation or experiment.

==Linear and rotational dynamics==
The study of dynamics falls under two categories: linear and rotational.  Linear dynamics pertains to objects moving in a line and involves such quantities as [[Physics:Force|force]], [[Physics:Mass|mass]]/[[Physics:Inertia#Mass and inertia|inertia]], [[Displacement (vector)|displacement]] (in units of distance), [[Physics:Velocity|velocity]] (distance per unit time), [[Physics:Acceleration|acceleration]] (distance per unit of time squared) and [[Physics:Momentum|momentum]] (mass times unit of velocity).  Rotational dynamics pertains to objects that are rotating or moving in a curved path and involves such quantities as [[Physics:Torque|torque]], [[Physics:Moment of inertia|moment of inertia]]/rotational inertia, [[Physics:Angular displacement|angular displacement]] (in radians or less often, degrees), [[Physics:Angular velocity|angular velocity]] (radians per unit time), [[Physics:Angular acceleration|angular acceleration]] (radians per unit of time squared) and [[Physics:Angular momentum|angular momentum]] (moment of inertia times unit of angular velocity).  Very often, objects exhibit linear and rotational motion.

For classical [[Physics:Electromagnetism|electromagnetism]],  [[Physics:Maxwell's equations|Maxwell's equations]] describe the kinematics. The dynamics of classical systems involving both mechanics and electromagnetism are described by the combination of Newton's laws, Maxwell's equations, and the [[Physics:Lorentz force|Lorentz force]].

==Force==
{{Main|Physics:Force}}
From Newton, force can be defined as an exertion or [[Physics:Pressure|pressure]] which can cause an object to accelerate. The concept of force is used to describe an influence which causes a [[Physics:Free body|free body]] (object) to accelerate. It can be a push or a pull, which causes an object to change direction, have new [[Physics:Velocity|velocity]], or to [[Physics:Deformation (mechanics)|deform]] temporarily or permanently. Generally speaking, force causes an object's [[Physics:Motion|state of motion]] to change.<ref name=Phys-tut-force>{{cite web| vauthors=Goc R| title = Force in Physics | date = 2005 | url=http://www.staff.amu.edu.pl/~romangoc/M3-1-force-physics.html| format = Physics tutorial | access-date = 2010-02-18| archive-url=https://web.archive.org/web/20100222050455/http://www.staff.amu.edu.pl/~romangoc/M3-1-force-physics.html| archive-date =2010-02-22| url-status =dead}}</ref>

==Newton's laws==
{{Main|Physics:Newton's laws of motion}}

Newton described force as the ability to cause a mass to accelerate. His three laws can be summarized as follows:
# '''First law''': If there is no net force on an object, then its [[Physics:Velocity|velocity]] is constant: either the object is at rest (if its velocity is equal to zero), or it moves with constant speed in a single direction.<ref name=first-law-shaums>{{Cite book| vauthors = Browne ME | title = Schaum's outline of theory and problems of physics for engineering and science | publisher = McGraw-Hill | location=New York | year = 1999| format = Series: Schaum's Outline Series| pages =[https://archive.org/details/schaumsoutlineof00brow/page/58 58]| url =https://archive.org/details/schaumsoutlineof00brow| url-access = registration| quote = Newton's first law of motion.| isbn =978-0-07-008498-8}}</ref><ref name=first-law-dmmy>{{Cite book| vauthors=Holzner S | title = Physics for Dummies | publisher = Wiley | location=Hoboken | year = 2005| pages =[https://archive.org/details/physicsfordummie00holz/page/64 64]| url = https://archive.org/details/physicsfordummie00holz| url-access = registration| quote = Newton's laws of motion| isbn = 978-0-7645-5433-9}}</ref>
# '''Second law''': The rate of change of linear momentum '''P''' of an object is equal to the net force '''F'''<sub>net</sub>, i.e., ''d'''''P'''/''dt'' = '''F'''<sub>net</sub>.<!-- Note #1: Object do not necessarily move in the direction of the net force....e.g. objects moving in a circle. Note #2: Beware! Both the acceleration and momentum formulations of Newton's second law are valid ''only'' for constant-mass systems. This is covered in the discussion below and in multiple references given. -->
#  '''Third law''': When a first body exerts a force '''F'''<sub>1</sub> on a second body, the second body simultaneously exerts a force '''F'''<sub>2</sub>&nbsp;= &minus;'''F'''<sub>1</sub> on the first body. This means that '''F'''<sub>1</sub> and '''F'''<sub>2</sub> are equal in magnitude and opposite in direction.

Newton's laws of motion are valid only in an [[Physics:Inertial frame of reference|inertial frame of reference]].

==See also==
*[[Physics:Statics|Statics]]
*Multibody dynamics
*[[Rigid body dynamics]]
*[[Physics:Analytical dynamics|Analytical dynamics]]

== References ==
{{Reflist}}

==Further reading==
*{{cite book|vauthors=Attenborough K, Postema M |date=2008 |title=A pocket-sized introduction to dynamics |url=https://hal.archives-ouvertes.fr/hal-03188303/document | location=Kingston upon Hull | publisher=University of Hull | doi=10.5281/zenodo.7504154|isbn=978-90-812588-3-8}} 
*{{cite web|author=Swagatam |date=25 March 2010 |title=Calculating Engineering Dynamics Using Newton's Laws |url=http://www.brighthub.com/engineering/mechanical/articles/111610.aspx |work=Bright Hub |access-date=2010-04-10 |url-status=dead |archive-url=https://web.archive.org/web/20110412013636/http://www.brighthub.com/engineering/mechanical/articles/111610.aspx |archive-date=April 12, 2011 }} 
*{{cite book |vauthors=Wilson CE |year=2003 |title=Kinematics and dynamics of machinery |publisher=Pearson | location=London |isbn=978-0-201-35099-9}}
*{{cite book|vauthors=Dresig HD, Holzweißig F |year=2010|title=Dynamics of Machinery: Theory and Applications|publisher=Springer | location=Heidelberg|ISBN=978-3-540-89939-6}}

{{Isaac Newton}}


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