Vomit comet

Shown below is the trajectory taken by an aircraft that is used to simulate weightlessness by its passengers over a short range of motion of the path (the data is from the Zero Gravity Corporation website). From this figure it is seen that the passenger feels weightless over a period of about 25 s near the maximum height of the trajectory. The aircraft is traveling 230 m/s at the maximum height (where the gravitational acceleration is known to be 9.79 m/s2).

The following is a video of a similar flight where the passengers experience "weightlessness".