Reply #8: Magnets would only act on ferrous materials.

[drm604]

Rotation could simulate gravity inside the sphere but only on and near the equator. The rest of the inside of the sphere would be weightless or near weightless (gravity would decrease as you move from the equator towards either of the poles). A wheel were you walk around the inside of the outer rim (like in 2001 a Space Odyssey) would probably be a more efficient use of materials.