Causing Friction

Often scientific breakthroughs in today's physics come on the scale of the incredibly small, incredibly large, incredibly fast or incredibly weird. But the field includes the study of very basic concepts that were known, even if not named, hundreds or even thousands of years ago. And many physicists like to study them, too, and uncover the weirdness that rests behind ideas we encounter far more often than we do quantum field theory.

One such idea is friction, and one such scientist is Andria Rogava of Ilia State University in Georgia -- the country, not the state. Rogava plays a lot of tennis and one day decided to stack the used tennis balls he had in his office, when scientific curiosity drove him to arrange them in several different configurations in order to see which ones were stable. Because tennis balls are not perfectly smooth, even when new, they have more friction when they touch each other. That means that making them move past each other requires more energy than it would to make smoother objects move past each other when touching. Physics World named Rogava's pictorial of his stacks one of its photos of the year, and the original blog entry from May can be found here.

The increased friction between tennis balls means that it takes more gravitational energy to make them fall apart than it would, say, racquetballs. Rogava tries to find configurations of the tennis ball stacks that use the friction to stabilize the stacks, even one with 25 tennis balls that stands nine levels high. He also includes a video of one of his stacks falling apart when only a single ball is removed in order to refute folks that say he glues the balls together somehow.