A good-quality flat plastic mirror, 2 × 3 feet (60 × 90 centimeters) or larger
A mirror stand (this can be anything that will support the mirror in an upright position and still allow someone to straddle it—for example, a ring stand or two with clamps and tape)
Secure your mirror in an upright position. One way to do this is to tape a ring stand to the back of the mirror. You want the mirror to be as vertical as possible and leave enough room for someone to be able to stand with one foot in front of the mirror and one foot in back.
To Do and Notice
Stand the mirror on the floor. Have your partner stand facing the mirror.
Straddle the mirror by placing one leg in front and one leg behind. Shift your weight to the foot behind the mirror. Next, lower yourself so your torso is at the top edge of the mirror, then lift your front leg and move it repeatedly toward and away from the mirror. To an observer, you’ll appear to be flying.
If you use this Snack as a demonstration, you can make the effect more dramatic by covering the mirror with a cloth, straddling the mirror, and then dropping the cloth as you “take off.”
What’s Going On?
If you stand with the edge of a large mirror bisecting your body, you will appear whole to a person who’s observing from the front. To the observer, the mirror image of the visible half of your body looks exactly like the real half that is obscured behind the mirror.
You look whole because the human body is symmetrical. The observer’s brain is tricked into believing that an image of your right side is really your left side. So just straddle the mirror, raise one leg, and you’ll fly!
You can try this out any place you find a good-sized mirror you can straddle or stand alongside—at home, in a department store, or in a dance studio with a doorway cut into a mirrored wall. Stand at the edge of the doorway so that half of your body is being reflected for a very convincing flight.
The cars that floated across the desert in the movie Star Wars each had a full-length mirror attached along their lower edge, hiding the wheels. A camera pointed at a car saw a view of reflected sand and shadow in the mirror. That's how the cars appeared to float above the sand.
Check out some things you can do with your Anti-Gravity Mirror in this episode of the Build Your Own Exploratorium video series.