Editing Vertical loop (section)

== Physics/mechanics ==
[[File:Walygator Comet looping.jpg|thumb|Most vertical loops are not circular.]]

Most roller coaster loops are not circular in shape. A commonly used shape is the [[clothoid]] loop, which resembles an inverted tear drop and allows for less intense G-forces throughout the element for the rider.<ref>{{cite web|url=http://fy.chalmers.se/LISEBERG/eng/loop_pe.html|archive-url=https://web.archive.org/web/20070827183113/http://fy.chalmers.se/LISEBERG/eng/loop_pe.html|archive-date=2007-08-27|title=Roller Coaster Loop Shapes|access-date=2008-08-13}}</ref> The use of this shape was pioneered in 1976 on [[The New Revolution (roller coaster)|The New Revolution]] at [[Six Flags Magic Mountain]], by [[Werner Stengel]] of leading coaster engineering firm Ing.-Büro Stengel GmbH.

On the way up, from the bottom to the top of the loop, gravity is in opposition to the direction of the cars and will slow the train. The train is slowest at the top of the loop. Once beyond the top, gravity helps to pull the cars down around the bend. If the loop's curvature is constant, the rider is subjected to the greatest force at the bottom. If the curvature of the track changes suddenly, as from level to a circular loop, the greatest force is imposed almost instantly (see [[Jerk (physics)|jerk]]). Gradual changes in curvature, as in the clothoid, reduce the force maximum (permitting more speed) and allow the rider time to cope safely with the changing force.<ref name="Physics for Scientists and Engineers"/>

This "gentling" runs somewhat contrary to the coaster's ''raison d'être''. [[Anton Schwarzkopf|Schwarzkopf]]-designed roller coasters often feature near-circular loops (in case of [[Zonga|Thriller]] even without any reduction of curvature between two almost perfectly circular loops) resulting in intense rides—a trademark for the designer.{{Citation needed|date=August 2013}}

It is rare for a roller coaster to stall in a vertical loop, although this has happened before. The Psyké Underground coaster (then known as Sirocco) at [[Walibi Belgium]] once stranded riders upside-down for several hours. The design of the trains and the rider restraint system (in this case, a simple lap bar) prevented any injuries from occurring, and the riders were removed with the use of a [[cherry picker]].{{Citation needed|date=August 2013}} A similar incident occurred on [[Demon (roller coaster)|Demon]] at [[Six Flags Great America]].<ref name=DemonIncident>{{cite news|title=Roller coaster stuck in loop at Six Flags|url=https://news.google.com/newspapers?id=JDpFAAAAIBAJ&dq=demon%20great-america&pg=6613%2C4120790|access-date=27 August 2017|newspaper=The Telegraph Herald|date=19 April 1998|agency=Associated Press}}</ref>