To understand how it works, Zenit employed an air cannon that he uses in his classes to teach students about drag and other forces that are important in fluid dynamics. He and his team loaded the cannon with squash balls and aimed it toward the corner of a room, near where the wall and floor meet. They fired balls at different speeds, angles and spots on the wall to get a sense of the conditions necessary for the nick shot to occur. They even varied the temperature of the ball, which affects its bounciness when it contacts the wall. 

Once they had a visual sense of what was happening, the team turned to Haneesh Kesari, an associate professor in Brown’s School of Engineering, for help modeling the phenomenon mathematically. Kesari, an expert in contact, adhesion and fracture of solids, has worked extensively to model forces in the brain associated with blows to the head. Zenit thought his work in contact mechanics might be useful in understanding the nick. 

“He looked at the videos and told me, ‘I know what’s happening,’” Zenit said. “So we developed a mathematical model explaining it.”

The model revealed that the nick shot happens when the ball maintains contact with the wall long enough to roll down the wall and contact the floor. 

“When the ball touches the floor while it’s still rolling down the wall, the floor introduces a new force that imposes a roll in the opposite direction,” Zenit explained. “The result is a mechanical frustration where the forces basically cancel each other out and the ball just gets stuck.”

For squash players, the findings suggest a strategy for increasing the likelihood of a nick: Hit the ball hard and with a bit of topspin. The speed of the ball increases the contact time with the wall, giving it more time to roll toward the floor. The topspin could enhance the roll, producing a greater range speeds with potential for a nick. 

The model has implications off the squash court as well, according to Zenit. 

“There may be situations where you want to dampen or frustrate a certain motion in a mechanical system,” he said. “This is a way of doing that. You could also do the opposite. You might be trying to prevent something from getting stuck, and this shows a way to avoid it.”

But Zenit says the real goal of the work is to demonstrate the power of science to explain the world. He works with an organization in Providence, Rhode Island called Squashbusters, which aims to build a community for kids — many from underserved groups — around the game of squash. In addition to playing the game, participants get homework help, guidance on planning for college, and character-building activities through community service. 

“This was really just an opportunity to connect squash with what we do as engineers,” Zenit said, “and to plant the seed in their in their brilliant minds that maybe they can be engineers, too.”