Final answer:
To balance a lever, magnitudes and directions of forces may change to ensure that the torques around the pivot are equal and opposite, hence achieving equilibrium. Newton's third law plays a role, showing that forces in pairs may cancel out when analyzed as a complete system.
Step-by-step explanation:
When balancing a lever, the magnitudes and directions of the forces involved can indeed change. To achieve a state of equilibrium on a lever, the sum of the torques around the pivot point must be zero. This condition implies that forces on opposite sides of the fulcrum may have different magnitudes, depending on the lengths of their lever arms. Directions of the forces also play a significant role; only the components of the forces perpendicular to the lever arms contribute to torque. Consequently, the magnitudes of the applied forces may be adjusted and sometimes even their directions are altered to ensure that the torques they produce balance out.
In accordance with Newton's third law of motion, the forces acting upon a lever occur in pairs of equal and opposite magnitudes; however, these only cancel out when considering the system as a whole. If a system of interest is chosen so that one force acts outside it, its corresponding reaction might not cancel within the system's boundaries, affecting the equilibrium.