INDUCING A CHARGE ON THE SURFACE OF A WALL

When you rub a balloon on someone's hair, a transfer of charge takes place.  The hair loses some electrons (remember that protons are stuck where the atom is), and the balloon gains some electrons.  This makes the hair stand up because the hairs are positive and repel each other.

 
You can't tell by looking that the balloon is negative, but you can see the effects of its negative charge... Imagine a wall surface:  for every positive charge, there's a negative charge.  It's neutral. 

(the whole wall is full of an equal # of positive and negative charges, but I only drew a few.

 
Now, if the balloon comes near the wall, the electrons of the atoms at the wall's edge migrate away from the balloon.  (remember, the electrons in a solid are more free to move than the protons are)


 This is why the balloon "sticks" to the wall.  Even before the balloon actually touches the wall, electrons are on the move away from the balloon.  This creation of charge is called induction.