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The Science Behind The Perfect Squash Kill Shot

A French squash-loving hydrodynamics scientist has finally answered a time-old question: why does hitting the ball near the corners make its trajectory utterly unpredictable?

The nick: impossible to catch (The World Squash Federation)
The nick: impossible to catch (The World Squash Federation)
David Larousserie

PALAISEAU - Who would have thought you could find a slingshot-type weapon in a research laboratory? And who would have though you could use it to study a sport -- squash -- that hasn't even been elevated to Olympic status? Yet that is exactly what has been taking place these few weeks at the hydrodynamic laboratory at the Polytechnic school (dubbed LadHyX) near Paris, France.

Sometimes, for your research to stand out, you need to identify the question that no one else has asked before. In this case the question goes like this: "In squash, why does hitting the ball near the corners make its trajectory unpredictable?" Squash is played in a small closed room; the goal is to hit a ball against a wall with a racket and to take advantage of the adjacent walls to destabilize the opponent.

"There have been fewer than ten articles on squash physics in the past 30 years and none have focused on the behavior of the ball that's hit against the "nick" where the sidewall and the floor meet," says Philippe Brunet, a hydrodynamics specialist from the CNRS at the university of Paris-VII. "Most notably, no one can explain the "nick" kill shot that only the greatest can pull off. The ball, after a first rebound, hits a nick at a downward angle and bounces back with a slow velocity along the wall or rolls parallel to the ground, making it impossible to hit."

Science to the rescue

For the researcher, who also plays the sport, this mystery had to be solved. He found two partners, Caroline Cohen and Baptiste Darbois-Texier, who are so passionate about sports and physics that they are writing a thesis on the subject.

Instead of playing on a real court with rackets and trying to hit balls into corners, they favored a more practical protocol: throwing balls with a slingshot into a Plexiglas corner and filming the experience with a high-speed camera at 3,000 frames per second.

An incubator enables them to heat the balls for better bounce, like they would be in real game conditions. At 70 °C, the balls bounce back with 70% of their initial speed. If they were cold, this percentage would be approximately 35%. The researchers sometimes heated up the projectiles so much that their volume doubled, causing them to bounce back as superballs - a property that wasn't relevant for this experience.

More than 100 shots later, the results were in.

Lessons learned

Lesson number one: the ball's slow rebound, measured as the ratio of the rebound speed and the initial speed, depends neither on the angle nor on the velocity. Everything depends on the impact of the ball on the first wall and then on the second wall when it bounces back. The ball slows down the most when it simultaneously touches both walls by hitting exactly at their intersection. At equal initial speed, around 100 kilometers-per-hour, the final velocity can be twice as slow.

Second lesson: it is possible, independently from speed and angle, to perform the perfect move by hitting slightly above the corner. The ball then sharply slows down and barely bounces back, rolling on the ground (if it hits the ground first, it hugs the wall). All it takes is a centimeter between both walls for the perfect rebound. Not an easy shot…

The explanation is in ball deformation. By hitting the wall before the ground, the ball flattens and deforms a lot more vertically than it does horizontally. It therefore rubs the wall more than it does the ground; the speed is lowered more in one direction than in another and it bounces back skimming the floor.

This was confirmed by another series of experiments that consisted in coating the balls with glycerol, a liquid that lowers object-friction. After a few stains on the lab coats and the Plexiglas, the team found that this coating made the perfect move even more difficult.

For the sport to remain spectacular, the court walls have to be the least slippery possible and the referees have to make sure the players don't wipe their sweaty hands in the corners, which would make the balls slide.

Read more from Le Temps in French.

Photo - The World Squash Federation

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Shame On The García Márquez Heirs — Cashing In On The "Scraps" Of A Legend

A decision to publish a sketchy manuscript as a posthumous novel by the late Gabriel García Márquez would have horrified Colombia's Nobel laureate, given his painstaking devotion to the precision of the written word.

Photo of a window with a sticker of the face of Gabriel Garcia Marquez with butterfly notes at Guadalajara's International Book Fair.

Poster of Gabriel Garcia Marquez at Guadalajara's International Book Fair.

Juan David Torres Duarte


BOGOTÁ — When a writer dies, there are several ways of administering the literary estate, depending on the ambitions of the heirs. One is to exercise a millimetric check on any use or edition of the author's works, in the manner of James Joyce's nephew, Stephen, who inherited his literary rights. He refused to let even academic papers quote from Joyce's landmark novel, Ulysses.

Or, you continue to publish the works, making small additions to their corpus, as with Italo Calvino, Samuel Beckett and Clarice Lispector, or none at all, which will probably happen with Milan Kundera and Cormac McCarthy.

Another way is to seek out every scrap of paper the author left and every little word that was jotted down — on a piece of cloth, say — and drip-feed them to publishers every two to three years with great pomp and publicity, to revive the writer's renown.

This has happened with the Argentine Julio Cortázar (who seems to have sold more books dead than alive), the French author Albert Camus (now with 200 volumes of personal and unfinished works) and with the Chilean author Roberto Bolaño. The latter's posthumous oeuvre is so abundant I am starting to wonder if his heirs haven't hired a ghost writer — typing and smoking away in some bedsit in Barcelona — to churn out "newly discovered" works.

Which group, I wonder, will our late, great novelist Gabriel García Márquez fit into?

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