Question

A lightweight metal ball hangs by a thread. When a charged rod is held near, the ball moves toward the rod, touches the rod, then quickly “flies away” from the rod. Explain this behavior.

Short answer

The ball flies away because the part of the charge of the rod is transferred to it and they become charged with the charge of same sign so they repel.

Step-by-step solution

Explanation of field.

In physics, a field is a region in which each point is connected with a physical quantity.

The quantity can be a number, as in the case of a scalar field like the Higgs field, or a vector, as in the case of fields that are connected with a force, like the gravitational field.

Explanation of ball remains neutral.

The charged rod's field induces a net opposing charge in the part of the ball closest to the rod and a net same charge in the part of the ball furthest away from the rod (the whole ball remains neutral). As a result, the rod attracts the closer part of the ball more than it repels the farther part, attracting the entire ball.

Reason of ball flies away.

When the ball and the rod make contact, the rod's charge is redistributed between the ball and the rod, which occurs very quickly.

The ball and the rod are then charged with the same sign of charge, and the net charge is dispersed on the ball's surface because it is conductive.

They repel each other because they now have the same charge sign, which is why the ball flies away.