What other ways besides using magnetic fields can we use to convert mechanical energy to electrical energy and vice versa?
The Van der Graaff generator is one example.

Image source: Wikimedia.

hollow metallic sphere (with positive charges)
electrode connected to the sphere, a brush ensures contact between the electrode and the belt
upper roller (Plexiglass)
side of the belt with positive charges
opposite side of the belt with negative charges
lower roller (metal)
lower electrode (ground)
spherical device with negative charges, used to discharge the main sphere
spark produced by the difference of potentials

Unlike most generators, applying voltage to it does not create a motor.