I understand how artificial gravity in space stations works. It is by normal force the wall exerts on the foot.
But I wonder how to start it in the first place. I just learned about centrifugation in a centrifuge. To start, the side-wall of the tube produce a tangential acceleration. Because of the inertia (tendency to go tangentially) of the material contained, normal force is thus needed to keep the material from going through the tube and keep it rotating in a circle.
But in the space station, there is no friction, so there is no way to create that tendency that produces the need for normal force in the first place.