A scanner floats when the artificial gravity in a shuttlepod fails
Artificial gravity is a collection of systems designed to mimic the gravity of a planet so that working in space is easier. One of the first uses of artificial gravity on Earth ships was in the 1990s on ships such as the SS Botany Bay and cryonics satellites. (TOS: "Space Seed"; TNG: "The Neutral Zone")
The basis of the Federation's artificial gravity technology was a "flying belt" found in a Slaver stasis box. (TAS: "The Slaver Weapon")
Elaysians have difficulty adjusting to the gravity of other worlds because their home planet has such low gravity. Without surgery, they need to utilize a special chair or braces to allow them to move. (DS9: "Melora")
Artificial gravity failures
After being attacked, the IKS Kronos One's artificial gravity field failed, and the whole ship experienced weightlessness for several minutes while assassins boarded and killed several members of the crew, including Chancellor Gorkon. (Star Trek VI: The Undiscovered Country)
Cardassian station Empok Nor's artificial gravity was off line when Garak first boarded the station, but he repaired it before the rest of the team came aboard. (DS9: "Empok Nor")
In 2374, a Species 8472 creature deactivated artificial gravity on deck 5 of the USS Voyager. (VOY: "Prey")
In 2376 when an electromagnetic lifeform was affecting ship's systems, the USS Voyager temporarily lost artificial gravity on Deck 9. The only injury reported was that "Ensign Mulcahey bumped his head on the ceiling." (VOY: "The Haunting of Deck Twelve")
When the Xyrillians were draining power from Enterprise NX-01, the gravity in Captain Archer's quarters went offline while he was taking a shower. (ENT: "Unexpected")
In 2152, the Enolians attacked and boarded Enterprise's shuttlepod, arresting Captain Archer and Commander Tucker and leaving the shuttle adrift. When Enterprise found it, the artificial gravity was off line. (ENT: "Canamar")