# When dominoes fall, how fast the row topples depends on friction

Computer modeling reveals the physics behind the chain reaction

Dominoes may seem like just fun and games. But understanding how they topple? That’s some serious science.

“It’s a problem that is so natural. Everybody plays with dominoes,” says David Cantor. He’s a researcher at Polytechnique Montréal in Quebec, Canada. He has a background in civil engineering. So Cantor set out to study the blocks.

Domino games are more fun with a buddy. Research on them would be too, Cantor thought. So he teamed up with a friend. That physicist, Kajetan Wojtacki, works at the Institute of Fundamental Technological Research. It’s part of the Polish Academy of Sciences in Warsaw.

The pair used a computer to model a row of dominoes collapsing. It’s a chain reaction: Each falling domino topples into the next, then the next and so on. And the speed of that cascade depends on friction, they learned.

The friction happens in two places, the pair report in the June Physical Review Applied. The dominoes rub together as they collide. They also slide along the surface on which they sit.

Their computer model showed how best to get a speedy collapse. The fastest fall took place when they spaced slippery dominoes close together on a rough surface, such as felt.

Slicker tiles mean less friction between dominoes. And that means less energy will be lost as they topple against each other. Sitting on a high-friction surface means the tiles don’t slide too far backward as they fall. Such backsliding would otherwise slow the cascading chain reaction.

In some model runs, the chain reaction stopped short. For instance, some dominoes spaced far apart on a slippery surface backslid so much that they never hit each other.

The domino duo used math to describe these computer-simulated outcomes. They came up with an equation that predicts the speed of collapse under different conditions. Its predictions matched results of previous experiments, too. Turns out, there’s serious science behind the satisfying spectacle.