Answer:
Due to repulsion.
Explanation:
Repulsion among electrons is responsible for fly off the pie pans from the Van de Graaff generator. When the globe of the generator charges up, the charge will move to the top part of the pie tin. The top region of pie tin accumulates charge and since it is not fixed at one place like upper half of the globe itself, it will be repelled by electrostatic forces between electrons that leads to fly off so we can say that similar charge of electrons is responsible for this fly off.
