Place the Styrofoam cup upside down. Insert the pencil through opposite sides of the cup approximately 1/2 inch from the top of the cup.
Push the pencil through the cup until there is an equal length of pencil on either sides of the cup.
Place the cup into the middle of a tinfoil plate. Move the cup so that one end of the pencil is hovering directly over the side of the plate. Glue the cup to the plate exactly where it sits. Allow the glue to dry for 10 minutes.
Cut an 8-inch length of string and tie a series of knots at one end until a small bulbous shape forms.
Wrap the opposite end of the string around the end of the pencil hovering over the side of the plate. Continue wrapping until the bulb shape at the other end of the string is a 1/2 inch away from the edge of the plate.
Tape the string to the pencil using masking tape.
Tear a 1-inch square piece of tinfoil and form into into a ball around the bulb-shaped end of the string.
Blow up a balloon and rub it against the surface of the Styrofoam plate for at least 30 seconds.
Lay the Styrofoam plate down and pick up the Styrofoam cup. Do not touch the tinfoil plate.
Set the tinfoil plate onto the Styrofoam plate. The tinfoil ball at the end of the string will levitate.