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There’s science behind that magic

By Jane Bollinger
January 29, 2014

HONESDALE, PA — Last Saturday afternoon, Bob Friedhoffer, aka Professor Bob, of Damascus Township, PA and New York City, took to the stage at The Cooperage to a room crowded with children to present his Scientific Magic Show. On the theory that young people not only like magic shows, but also want to know how things work, Friedhoffer entertained everyone—children and adults alike—with a collection of magic tricks. But then, unlike other magicians, he revealed not only how he accomplished the tricks, but also some of the scientific principles involved.

In one trick, the Professor began by partially filling a clear plastic cup with water. Next, he placed an ordinary postcard on the open top of the cup, and then, with one hand holding the cup and the other holding the postcard in place, he turned everything upside down. After saying the magic words “Honesdale is cool,” (much to the amusement of the audience), he removed his hand from the postcard, and there it stayed, holding the water in the inverted cup. Not a drop was spilled. A small voice from the back of the room was heard to say, “That’s cool,” and another, “It’s magic.” The audience applauded. At the end of the trick, in response to a few more magic words, the postcard fell from the cup and the water spilled into a bucket below.

Next, the Professor revealed the secret of the trick: the cup had been prepared beforehand by drilling a hole in its side near the bottom of the cup, but when he filled the cup, his thumb covered the hole preventing the water from escaping, and when he turned the cup upside down (still keeping his thumb over the hole) a vacuum was created, holding the postcard (and thus the water, too) in place. “The air pressure inside the glass is less than the air pressure outside the glass, and the pressure outside the glass is so strong it holds the postcard in place,” Professor Bob told the crowd. When he suddenly released his finger from the hole in the cup, the postcard fell and the water spilled out,. “Your perception, or what you think you see, is not necessarily what is happening,” he said. Later he revealed that this trick really “is a very old science demonstration.”

Among the many scientific principles Friedhoffer pointed out during the show were explanations of the nature of gravity and balance; the properties of elasticity and adhesion; a mention of Isaac Newton’s three principles of motion, and of Copernicus’ 14th century theory that the earth travels around the sun and not vice versa; and more.