Force fields come in 2 varieties plasma shields and magnetic fields. Magnetic fields are usually for personal protection and vehicle protection, and are meant to cause projectiles and charged particle beams to be deflected away from the target. Plasma shields also use strong magnetic fields but also release super heated plasma that is held in place by the field to incinerate projectiles. This gives added protection for projectiles with high enough inertia to not be deflected enough to miss. Plasma Shields are only usable on space ships.