NASA has a zero gravity research facility. The facility is housed in Brook Park, Ohio, and it has been in use since 1966.
NASA's Zero-G facility is the biggest one of it's kind in the world, providing 5.18 seconds of microgravity, or relative near weightlessness. On Earth, microgravity is only possible when something is free falling. NASA has two drop towers at the Brook Park site, but only one is a zero-gravity tower. Equipment being studied in the free fall tower drops 432-feet before being stopped by the tower's decelerator cart. There are size and weight limits on items being dropped by researchers in the tower.