Increasing friction with the surface beneath speeds up the wave because it reduces domino backsliding, allowing each one to strike its neighbor higher up, where the impact is more effective, the researchers believe. (Clip from Sandlin’s first dominoes video.)įrom their comprehensive campaign of 1210 simulations that included 200 dominoes in each, Cantor and Wojtacki found that, when the spacing is half of the domino thickness, domino-surface friction and domino-domino friction play competing roles: Increasing the friction between dominoes causes the wave front to slow down because friction absorbs some energy from the wave of motion. Sandlin/Smarter Every Day On a surface with friction, there is much less backsliding. Cantor and Wojtacki performed simulations that would fully control these parameters in hopes of better explaining observations.ĭ.
Researchers have previously performed experiments and simulations and developed theories for domino toppling, but no one has systematically studied how domino-surface friction, domino-domino friction, and domino spacing affect the wave speed. But experimental limitations prevented him from fully explaining the effects of friction on the wave speed. Sandlin observed that a slippery surface can cause a domino to slide backward while falling forward and thus hit the next domino somewhat lower down when compared with dominoes on high-friction felt. He also saw surprising anomalies, such as cases where the train of toppling dominoes would abruptly stop. He determined that the wave of falling dominoes moves slightly faster on felt than on a slippery hardwood floor. Sandlin recorded a series of domino toppling experiments with a high-speed camera and quickly discovered just how complex the problem is. They also found that one of the coefficients behaves similar to friction in granular systems such as piles of sand or pharmaceutical pills, suggesting that the domino simulations may provide insights into other situations where friction is important.Ī YouTube video by engineer Destin Sandlin (on his channel Smarter Every Day) inspired David Cantor of Montreal Polytechnic and Kajetan Wojtacki of the Institute of Fundamental Technological Research of the Polish Academy of Sciences in Warsaw to study dominoes. The researchers found that, in some cases, these two friction coefficients play competing roles in determining the speed of the domino cascade. But new numerical simulations get a step closer by untangling the influence of two types of friction-one between neighboring dominoes and the other between each domino and the surface beneath it. (See videos below.) ×ĭespite the apparent simplicity of toppling dominoes, physicists still don’t have a complete model of the phenomenon. New simulations reveal the role of friction in the seemingly simple mechanics of domino toppling.
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