Air time is the feeling of weightlessness or negative gravity force experienced on a roller coaster or other amusement rides. On roller coasters this feeling is usually achieved by the train going over a hill. Hypercoasters such as Magnum XL-200 at Cedar Point and Nitro at Six Flags Great Adventure are known for their large amounts of air time. In addition, many wooden roller coasters, such as Balder at Liseberg, The Voyage at Holiday World, and Shivering Timbers at Michigan's Adventure are known for their air-time.
Air-time is caused by inertia of the train and the riders. As the train goes over a hill, the mass of the riders tends to resist the downward motion of the ride vehicle, resulting in riders being briefly lifted out of their seats. The amount of airtime caused by a ride is dependent on the velocity of the train, gravity, and the radius of the track transition. Zero gravity is achieved when the downward acceleration is equal to that of gravity, while negative G-forces are caused when the downward acceleration is greater than that of gravity.
Roller coaster enthusiasts differentiate between different types of air-time. Floater air-time is caused by the riders experiencing weightlessness or zero gravity while ejector airtime is caused by negative G-forces.