Jennifer “Juniper” Jairala grips the rail of one of the water rides at Universal Studios’ new theme park in Osaka, Japan. She knows the drop is coming, but she still feels a thrill as the boat she is on plunges over the edge. Unlike most people who ride the roller coasters and water rides at the new theme park, Jairala is more than just a casual observer. As one of the park’s ride-show engineers, Jairala helps design, assemble, and test some of the scariest rides in the world. You might even call her the Queen of Scream.

How did Jairala get what she calls her dream job? She says it all started with a childhood interest in how things work. While she was growing up in Chicago, Jairala was constantly trying to fix anything in her house that broke. Moreover, she was a good student. She says that when people asked her what her favorite subject was, she would reply, “All of them.” After graduating from high school, Jairala went to Cornell University, where she earned a bachelor’s degree in mechanical engineering. Now she works for one of the biggest theme-park corporations in the world.

Although the theme park where Jairala works has been open for approximately a year, she has worked there for about two years. Before the park opened, she oversaw the construction of the rides. Although customers are hoping to be scared on the rides, the park obviously doesn’t want to really imperil its customers. It was Jairala’s job to inspect the rides at each step to make sure they were being built correctly. The rides go through many tests before any human passenger is allowed to climb aboard. For example, the roller coasters are first tested with sandbags that each weigh about the same as a human passenger. In addition, Jairala and other engineers took numerous test rides. Jairala enjoys the thrill of testing a new ride, but she keeps safety foremost in mind.

Roller-coaster engineers like Jairala say the best part of designing roller coasters is turning fear into fun. It all starts with illusion. Amusement-park designers and engineers always try to make roller coasters look and feel as frightening as possible without the rides actually being dangerous. They sometimes give the coaster an aged appearance. They might play strange noises over the sound system or run the coasters through dimly lit passages. Then most coasters tantalize the rider with a slow climb to the top before the first drop. Wooden coasters have a natural, but safe, tendency to clickity-clack, shake, tremble, and whine as the cars climb. It’s all part of what makes the coasters so much fun. Though coasters usually travel slower than the speed limit on most highways, they seem faster. The closeness of things flashing by and the jerky, rough ride make passengers feel as if the roller coaster is rocketing out of control. Not all of the coaster’s effects are an illusion. On some drops passengers are subjected to forces of gravity (called G’s) more than four times as strong as normal. Loops and corkscrews turn the riders around, literally forcing the breath out of them.

There is much more to planning amusement-park rides than just figuring out how to scare people. Roller-coaster engineers must keep other factors in mind when building a ride. They must build a ride that is scary but will entice customers to keep coming back. It wouldn’t be good for park business if a rider rode a coaster once and decided never to ride it again. Therefore, designers look for a balance.

Jairala and other engineers must also pay attention to the length of the ride. The physical forces of gravity determine how long the coaster’s momentum will keep it going. No matter how tall the coaster is, rides will usually last only about a minute after the first drop begins. Customers who sometimes must wait for more than an hour to ride want their money’s worth. With this in mind, engineers sometimes extend the length of a ride by using machinery to pull the coaster back up for more drops.

On the other hand, rides can’t last too long. Engineers like Jairala must keep in mind how many thrills passengers can take in the space of a few minutes. It’s also important to limit the length of a ride so that people aren’t kept waiting. Theme parks prefer that customers purchase snacks and souvenirs rather than wait in a line. Shorter waits also encourage customers to return to the park in the future. In addition, engineers must consider how easy it is to get into and out of the rides and how to best accommodate large groups that want to ride together.

Now that Universal Studios Japan is open, Jairala spends most of her time testing and checking rides to ensure that they are working properly and are safe. However, she is still able to help with the design of the new rides that are constantly being planned for the park. While Jairala hopes to continue building thrill rides, she also wants to continue her education. She plans to someday go back to school for an advanced college degree. Right now, though, she’s happy to see another part of the world and work in her dream job.