Emory Report

April 26, 1999

Volume 51, No. 29

Peering into a cup of joe gave Perkowitz a book idea That water may have tenacity and cohesion together is quite clearly shown where the [water] drop before it falls becomes elongated as possible, until the weight of the drop renders the tenacity by which it is suspended so thin that this tenacity, overcome by the excessive weight, suddenly yields and breaks. -Leonardo DaVinci Leonardo DaVinci had an intense interest in surface tension, the physical force that holds together a drop of water. Under certain conditions this same force allows water mixed with air to form a most elegant and appealing substance: foam. Yet even before DaVinci pondered foam-his interest yielding to drawings of violent and frothy water--the ancient Greeks were equally enthralled with its mysteries. In their mythology, the world has its beginning in a foamy turmoil, thought to be the sperm of the Titans who formed creation. Standing in the kitchen of his Atlanta home, Candler Professor of Physics Sidney Perkowitz had just gone through his morning ritual of preparing cappuccino. As he looked into the cup and inhaled the aroma, a thought struck him. "When I looked at the froth, [it was] a huge foam," he recalled. "It's air and milk, and you get a mass of bubbles. I make this thing. I look at it every morning, and I realize that it's something we take for granted, but really a complicated system. What's really going on here?" His interest piqued, Perkowitz wrote a magazine article on the subject. "It was going to be called 'The Theory of Cappuccino,'" Perkowitz said. But when he showed the piece to his literary agent, the agent suggested expanding the article into a book. Describing the complexities of the common bubble, Perkowitz said, "It's something like a solid and something like a liquid-it's not like a book, which is entirely solid, or a piece of wood. And it's certainly not like water. That's one of the things about how foam behaves; it's not entirely understood why it has the mechanical properties it does: somewhat solid-like, somewhat liquid-like." Perkowitz addresses wide-ranging topics in his book-foam in food and drink, the mathematics of bubbles, how foam works, foam in history and art, the history of foam technology and quantum foam--in short, a host of interesting chapters, all about a unique material and all meant to grab the attention of scientist and layman alike. To research his idea, Perkowitz and some of his students poured over scientific papers, history books and literature. Some information could be found on the web or in the library, but he also visited researchers at the University of California at Los Angeles and the University of Washington. Perkowitz also looked in less likely places. He spoke with a French chef about the difficulty of making soufflé, and lest some readers doubt the complexities of foam, the culinary master made it quite clear that a new recipe for this whipped dessert may take the most experienced chef 20 or 30 tries to achieve "perfection." "As a cooking challenge, it's one of the hardest things people can do," Perkowitz explained. The stories he uncovered all reveal highly fascinating facts, such as the genesis of modern whipped cream dispensers. During World War II, Perkowitz related, American forces quickly came up against an unforeseen foe-the mosquito. To protect troops from bites and possibly malaria, American scientists devised a bug "bomb." "There was a strong container filled with an insecticide--the liquid--and also with a gas. You would press a valve and out would come the liquid as a mist or a fog, an aerosol," Perkowitz said. Soon after, commercial scientists found other uses for the bug bomb. "It became a shaving cream dispenser and a little whipped cream dispenser," he said. Perkowitz also discovered exotic foams such as a metal one used by the United States in spy satellites. Scientists placed extremely cold, liquid helium in sensitive infrared devices that tracked missile launches around the world. As the satellites traveled through space, the metal foam kept the liquid from sloshing around. NASA also is using a novel foam made from glass. Last February Project StarDust launched a spacecraft that will travel 3 billion miles and collect gas and dust from a comet. Glass foam mounted on the spacecraft will act as a sponge, capturing material that NASA scientists hope will provide information about the origins of the solar system. The StarDust spacecraft is due back to Earth in the year 2006, but for those interested in it and other intriguing, "foamy" issues, Perkowitz's book will arrive in bookstores sometime early next year. --Paul Thacker Return to April 26, 1999, contents page