Training to become an astronaut requires an applicant to endure physically demanding and stressful tests -- various machines and simulators measure each trainee's response to the rigors of space travel. Today, an entirely unrelated industry uses many of these simulators and other devices for a different purpose -- entertainment.

Photo courtesy of Zero Gravity Corporation Playing catch with a fellow passenger in a low-gravity environment

Few of these simulators appeal to the general public more than the zero-gravity flight. Almost everyone dreams of floating effortlessly like astronauts in space. Currently, NASA uses a modified C-9 plane to create simulations of a weightless environment, both for training purposes and to conduct weightlessness experiments (without the enormous costs of space travel). Until recently, only a select few had the privilege of experiencing these flights. Today, a company called Zero Gravity Corporation (ZERO-G) offers this experience to the general public.

Video Gallery: In Thrust We Trust ­­­See how zero gravity works in this news video from Reuters. Famed physicist Stephen Hawking took air travel to new heights as he left gravity and his wheelchair, floating weightless in a specially designed jet that dives through the sky to give passengers an experience of zero gravity. Watch this video about gravity with BMX superstar Chad Kagy on HowStuffWorks. See how NASA and Kagy explain the role of gravity in fun and science in this video from NASA. Watch this video about aircraft engines on HowStuffWorks. Japan Airlines was one of the first companies to receive GE's record-breaking aircraft engines. See how airplane engines work in this video from GE.

In this article, we'll learn about gravity, free-falling and what it's like to board the so-called "vomit comet." We'll start with what it's like to experience weightlessness.

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