A neutral (unchanged) metal ball is suspended using a non-magnetic string. A positively charged insulating rod is placed near the ball which is observed to be attracted to the rod. This is because

When a positively charged insulating rod is brought near a neutral metal ball, the ball is attracted due to electrostatic induction [t1][t5]. In a conductor like a metal ball, electrons are free to move [c5][t6]. The positive charge on the rod exerts an attractive force on the negatively charged electrons within the ball, causing them to migrate toward the side closest to the rod [t1][t9]. This results in a rearrangement of electrons, creating a negative charge concentration near the rod and leaving the far side positively charged—a process known as polarization [t1][t8]. Although the ball remains net neutral because no charge is transferred, the attractive force between the rod and the closer negative charges is stronger than the repulsive force from the more distant positive charges, leading to a net attraction [t1][t5][t7].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > 11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE > p. 173
2. [2] https://www.sciencedirect.com/topics/engineering/charged-object