The greater the curvature of the part given electrostatic charge, the more of a deflection a given motion of the balloon will produce. It is possible to move the balloon so fast that no deflection is seen even though a slower motion produces a strong deflection. This can be explained using inertial considerations. Other static charge devices could easily be substituted for the balloon. Using the glass rod and silk set-up might make it easier to control, but would make it harder to work out the curvature effect on local potential fields.
Students ought to try diagonal motion relative to the plane of rotation also.
The goal is to establish that the vertical component of the charged particle motion relative to the magnet is what produces a horizontal deflection. Part 2-3 Students will work with a circuit producing a known DC current and measure the magnetic field induced by a long straight wire. The wire will need to be oriented vertically to be most convenient for magnetometer readings. Appeal to symmetry to simplify data taking. Work with circles of increasing radius to make the maps for different radial distances.