Editing Acceleration (section)

{{Short description|Rate of change of velocity}}
{{About|acceleration in physics}}
{{Redirect|Accelerate}}
{{Use British English|date=January 2025}}
{{Infobox physical quantity
| name = Acceleration
| image = Gravity gravita grave.gif
| caption = {{longitem|In vacuum (no [[Drag (physics)|air resistance]]), objects attracted by Earth gain speed at a steady rate.}}
| symbols = '''a'''
| unit = [[Metre per second squared|m/s{{sup|2}}, m·s{{sup|−2}}, m&nbsp;s{{sup|−2}}]]
| derivations = <math qid=Q11376>\mathbf{a} =  \frac{d\mathbf{v}}{dt} = \frac{d^2\mathbf{x}}{dt^2}</math>
| dimension = wikidata
}}
{{Classical mechanics |Fundamentals |width=20.5em}}

[[Image:DonPrudhommeFire1991KennyBernstein.jpg|thumb|upright=1.4|[[Drag racing]] is a sport in which specially-built vehicles compete to be the fastest to accelerate from a standing start.]]

In [[mechanics]], '''acceleration''' is the [[Rate (mathematics)|rate]] of change of the [[velocity]] of an object with respect to time. Acceleration is one of several components of [[kinematics]], the study of [[motion]]. Accelerations are [[Euclidean vector|vector]] quantities (in that they have [[Magnitude (mathematics)|magnitude]] and [[Direction (geometry)|direction]]).<ref>{{cite book |title=Relativity and Common Sense |first=Hermann |last=Bondi |pages=[https://archive.org/details/relativitycommon0000bond/page/3 3] |publisher=Courier Dover Publications |year=1980 |isbn=978-0-486-24021-3 |url=https://archive.org/details/relativitycommon0000bond/page/3 }}</ref><ref>{{cite book |title=Physics the Easy Way |pages=[https://archive.org/details/physicseasyway00lehr_0/page/27 27] |first=Robert L. |last=Lehrman |publisher=Barron's Educational Series |year=1998 |isbn=978-0-7641-0236-3 |url=https://archive.org/details/physicseasyway00lehr_0/page/27 }}</ref> The orientation of an object's acceleration is given by the orientation of the ''net'' [[force]] acting on that object. The magnitude of an object's acceleration, as described by [[Newton's second law]],<ref>{{cite book |title=The Principles of Mechanics |first=Henry |last=Crew |publisher=BiblioBazaar, LLC |year=2008 |isbn=978-0-559-36871-4 |pages=43}}</ref> is the combined effect of two causes:
* the net balance of all external [[force]]s acting onto that object — magnitude is [[Direct proportionality|directly proportional]] to this net resulting force;
* that object's [[mass]], depending on the materials out of which it is made — magnitude is [[Inverse proportionality|inversely proportional]] to the object's mass.

The [[International System of Units|SI]] unit for acceleration is [[metre per second squared]] ({{nowrap|m⋅s<sup>−2</sup>}}, <math>\mathrm{\tfrac{m}{s^2}}</math>).

For example, when a [[vehicle]] starts from a [[Wikt:standstill|standstill]] (zero velocity, in an [[inertial frame of reference]]) and travels in a straight line at increasing speeds, it is accelerating in the direction of travel. If the vehicle turns, an acceleration occurs toward the new direction and changes its motion vector.  The acceleration of the vehicle in its current direction of motion is called a linear (or tangential during [[circular motion]]s) acceleration, the [[reaction (physics)|reaction]] to which the passengers on board experience as a force pushing them back into their seats. When changing direction, the effecting acceleration is called radial (or centripetal during circular motions) acceleration, the reaction to which the passengers experience as a [[centrifugal force]]. If the speed of the vehicle decreases, this is an acceleration in the opposite direction of the velocity vector (mathematically a [[negative number|negative]], if the movement is unidimensional and the velocity is positive), sometimes called '''deceleration'''<ref>{{cite book |title=Mechanics |author1=P. Smith |author2=R. C. Smith |edition=2nd, illustrated, reprinted |publisher=John Wiley & Sons |year=1991 |isbn=978-0-471-92737-2 |page=39 |url=https://books.google.com/books?id=Zzh_unG7OAsC}} [https://books.google.com/books?id=Zzh_unG7OAsC&pg=PA39 Extract of page 39]</ref><ref>{{cite book |title=Physics, Volume One: Chapters 1-17, Volume 1 |author1=John D. Cutnell |author2=Kenneth W. Johnson |edition=1st0, illustrated |publisher=John Wiley & Sons |year=2014 |isbn=978-1-118-83688-0 |page=36 |url=https://books.google.com/books?id=PJWDBgAAQBAJ}} [https://books.google.com/books?id=PJWDBgAAQBAJ&pg=PA36 Extract of page 36]</ref> or '''retardation''', and passengers experience the reaction to deceleration as an [[inertia]]l force pushing them forward.  Such negative accelerations are often achieved by [[retrorocket]] burning in [[spacecraft]].<ref>{{cite book |author1=Raymond A. Serway |author2=Chris Vuille |author3=Jerry S. Faughn |title=College Physics, Volume 10 |year=2008 |publisher=Cengage |isbn=9780495386933 |page=32 |url=https://books.google.com/books?id=CX0u0mIOZ44C&pg=PA32}}</ref> Both acceleration and deceleration are treated the same, as they are both changes in velocity. Each of these accelerations (tangential, radial, deceleration) is felt by passengers until their relative (differential) velocity are neutralised in [[frame of reference|reference]] to the acceleration due to change in speed.