Hi pf, please could someone explain how a human centrifuge enables astronauts to experience a simulated gravity effect. I understand that if a centrifuge machine has a centripetal acceleration of 20 m/s^2 then they will feel a force of 2g. The thing that confuses me is that they are spun on a horizontal plane so in the y-plane where gravity normally acts there is no centrifugal effect yet the astronauts on the human centrifuge find it difficult to lift their hand up (in the y-plane). Surely if your being spun on a horizontal plane you only feel the simulated gravitational effect across your body? Also, if the human centrifuge goes too fast the person inside is at risk of dying apparently. I was just wondering what would actually kill you since there is no such thing as a centrifugal force. Would they be killed by the centripetal force pushing against them or by their inertia or both? Thanks people!