Force exerted on an uncharged particle in a uniform magnetic field?

The item will distort the magnetic field (because the field lines would "prefer" to travel through the iron than free space). It will experience forces/torques to enable more field lines to pass through the object.

In the case of a (initially) uniform magnetic field and a symmetrical sphere, there will be zero force because there is no difference in any position or orientation.

Whereas a normal magnet creates a very non-uniform field. The increasing strength of the field near the poles creates the lower potential (force toward) at those locations.

Typically a uniform magnetic field will NOT exert a net force on a magnetic dipole. It will cause it to rotate. A field gradient is needed to create a net force on the com of the magnetic material. Of course that analysis requires (1) the external field to be uniform (which it is based on your description) and (2) the dipole to have a fixed value. When you place unpolarized material in a field it will alter the material and that may create an opportunity for a force to be set up. This type of problem is addressed in most undergrad physics books to some degree of approximation. More elaborate treatments can be found in upper level EM physics texts.

The ball will experience no net force because electrons in the ball are not moving. The force would have been exerted if the ball was moving(thus the electrons would move along with it) and you know that moving electrons experience a force $q ,vec{v}times vec{B}$