Inversions in roller coasters are points where the riders are turned upside down so their feet are above their heads. There are no requirements as to the angle or how the riders are turned. For instance, traditional roller coaster inversion has a loop that turns the riders upside down, while contemporary fourth-dimension roller coasters have mechanisms that invert the cars of the roller coaster and the track separately, so that the riders can experience two types of inversion--the inversion of the car and the inversion of the tracks when the roller coaster goes upside down. Most roller coaster inversions have tracks in the shape of a clothoid, which resembles the shape of the inner circle of a Venn diagram. Because it's narrower, the clothoid loop requires less energy to complete the loop, which reduces the uncomfortable pressure caused by the force of acceleration on the rider.
The first vertical inversions produced serious injuries and deaths in their riders. For instance, one of the earliest roller coasters with a vertical inversion, the Flip-Flap Railway built in Coney Island in 1898, caused riders' necks to snap while going through the inversions. This was due to the high levels of gravitational force the riders experienced while turning upside down. As fear of the dangers of inverted roller coasters spread, their popularity declined until innovations during the 1970s. Arrow Dynamics created the first safe, steel track roller coaster with corkscrew inversion. Since the 1970s, many roller coasters with inversions have been built throughout the world.
Roller coasters have many types of inversions. The most common types are the basic circle loop and the vertical loop. The basic circle loop is one inverted track on a roller coaster, while the vertical loop track inverts in an elliptical shape. The inverted loop is also another form of inversion that simply appears like a twist in the track and briefly turns the riders upside down. Another style is the corkscrew loop, which is a series of vertical loops.
Many famous roller coasters have inversions. For instance, the Son of Beast roller coaster at Kings Island in Ohio opened to the public in 2000. It was the first wooden roller coaster with a vertical loop inversion. The X, which premiered in 2002, was the first fourth dimension roller coaster in the world. Located at Six Flags Magic Mountain, it rotates and inverts riders independently of the track, which is also inverted. Similarly, the Eejanaika in Japan, also a fourth dimension roller coaster built in 2006, holds the Guinness Book of World Records (as of this article's publication) for the roller coaster with the most inversions: 14.
