What you will need:
1) Two Styrofoam cups
2) Piece of wool or cloth
3) Willing victim/helper
4) Fun Fly Stick ® toy
Begin by talking about static electricity and how two objects with the same charge will repel or “push away” from each other. If you have a Fun Fly Stick ® toy, demonstrate this effect now.The Fun Fly Stick is a toy that uses static electricity to charge a piece of Mylar, causing it to float as you hold the stick underneath it. This is a great way to "suck" your victim into believing that what you are about to show them actually works. If you do not have a Fun Fly Stick, just explain how two objects with the same electrical charge will repel each other.
Give your victim a Styrofoam cup. Take your cup and rub it on the piece of cloth for a few seconds. Now quickly rub your other hand on the cloth while explaining that you are building up a negative charge from all of the electrons in both your hands and the cup.
Without their knowledge, Carefully press your thumb into the back of the cup so that it is stuck to your thumb
While facing your victim, hold one hand under the cup and the other hand (the one with your thumb inserted into the cup) behind and somewhat over the top of the cup. Make sure that your thumb is pointing directly at the person so that it remains hidden behind the cup. Now move your hands apart so that your thumb is holding the cup in between your hands making it appear to float. You can add to the effect by slightly moving your hands around the cup and moving your thumb just slightly so that it appears that your hand movements are affecting the cup as it "floats" between your hands.
Watch as your victim now tries over and over again and, no matter how hard they try, they will not be able to get their cup to float.