Rub the balloon on your hair, a pet's fur or, if available, a bit of wool cloth. The balloon will now have a net-negative charge. Tap the balloon against the pith ball. Make sure that the balloon is the only item that touches the pith ball. Some of the charge from the balloon should transfer to the pith ball. If necessary, rub the balloon with hair, fur, or wool again to make sure the balloon is very charged. Once data collection begins, do not change the amount of charge on either the balloon or the pith ball. Put the center of the balloon some distance r from