A negatively charged plastic rod will negatively charge a pith ball when in contact. My understanding is that the extra electrons transfer from the rod to the ball, thus giving the pith ball a negative charge. When an electrophorus is charged and the metal pan is put on top, it doesn't become charged. At least not until the metal is grounded by user. How is this different than the rod and pith ball? The pith ball isn't grounded, so why is there a transfer of charge? Is it because while holding the rod, the rod is grounded? But wouldn't that mean charge is flowing through the rod even though the rod is an insulator?