Editing Force (section)

=== Tension ===
{{main|Tension (physics)}}
Tension forces can be modeled using ideal strings that are massless, frictionless, unbreakable, and do not stretch. They can be combined with ideal [[pulley]]s, which allow ideal strings to switch physical direction. Ideal strings transmit tension forces instantaneously in action–reaction pairs so that if two objects are connected by an ideal string, any force directed along the string by the first object is accompanied by a force directed along the string in the opposite direction by the second object.<ref>{{cite web
|title=Tension Force
|work=Non-Calculus Based Physics I
|url=http://www.mtsu.edu/~phys2010/Lectures/Part_2__L6_-_L11/Lecture_9/Tension_Force/tension_force.html
|access-date=2008-01-04
|archive-date=2007-12-27
|archive-url=https://web.archive.org/web/20071227065923/http://www.mtsu.edu/~phys2010/Lectures/Part_2__L6_-_L11/Lecture_9/Tension_Force/tension_force.html
|url-status=dead
}}</ref> By connecting the same string multiple times to the same object through the use of a configuration that uses movable pulleys, the tension force on a load can be multiplied. For every string that acts on a load, another factor of the tension force in the string acts on the load. Such machines allow a [[mechanical advantage]] for a corresponding increase in the length of displaced string needed to move the load. These tandem effects result ultimately in the [[conservation of energy|conservation of mechanical energy]] since the [[#Kinematic integrals|work done on the load]] is the same no matter how complicated the machine.<ref name=FeynmanVol1 />{{rp|at=ch.12}}<ref name=Kleppner /><ref>{{cite web |last=Fitzpatrick |first=Richard |title=Strings, pulleys, and inclines |date=2006-02-02 |url=http://farside.ph.utexas.edu/teaching/301/lectures/node48.html |access-date=2008-01-04}}</ref>