So the homework question is this. In a donut shaped space station that is rotating, what is the force on an astronaut inside the space station (he is on the outside) in both an inertial frame, and the frame of the space station. Intuitively in the frame of the space station the two forces are a)The centripital force and b) the normal force of the space station. However when i try to think of the forces on the astronaut in a inertial frame my mind goes blank. Any ideas?