Astronauts and space enthusiasts have tried for a long time to figure out ways in which gravity could be somehow simulated during a long-term space mission.
1) Why might that be a useful thing to do?
2) One method that's been considered for years (though never done yet, for reasons we'll discuss shortly) is to have your spacecraft, space station, etc. be equipped to rotate around some central axis. Explain in as much detail as you can how rotating your spacecraft can help give the occupants the sensation of weight.