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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The Food Truck, A Sign That The White And Wealthy Are Moving In

In San Diego, California, a researcher tracked how in the city's low-income neighborhoods that have traditionally lacked dining options, when interesting eateries arrive the gentrification of white, affluent and college-educated people has begun.

Balboa Park Spring Fling Food Truck festival

San Diego Food Trucks via Facebook
Pascale Joassart-Marcelli

SAN DIEGO — Everybody, it seems, welcomes the arrival of new restaurants, cafés, food trucks and farmers markets.

What could be the downside of fresh veggies, homemade empanadas and a pop-up restaurant specializing in banh mis?

But when they appear in unexpected places – think inner-city areas populated by immigrants – they're often the first salvo in a broader effort to rebrand and remake the community. As a result, these neighborhoods can quickly become unaffordable and unrecognizable to longtime residents.

An appetite for gentrification

I live in San Diego, where I teach courses on urban and food geographies and conduct research on the relationship between food and ethnicity in urban contexts.

In recent years, I started to notice a pattern playing out in the city's low-income neighborhoods that have traditionally lacked food options. More ethnic restaurants, street vendors, community gardens and farmers markets were cropping up. These, in turn, spurred growing numbers of white, affluent and college-educated people to venture into areas they had long avoided.

This observation inspired me to write a book, titled The $16 Taco, about how food – including what's seen as "ethnic," "authentic" or "alternative" – often serves as a spearhead for gentrification.

Take City Heights, a large multi-ethnic San Diego neighborhood where successive waves of refugees from places as far away as Vietnam and Somalia have resettled. In 2016, a dusty vacant lot on the busiest boulevard was converted into an outdoor international marketplace called Fair@44. There, food vendors gather in semi-permanent stalls to sell pupusas, lechon (roasted pig), single-sourced cold-brewed coffee, cupcakes and tamarind raspado (crushed ice) to neighborhood residents, along with tourists and visitors from other parts of the city.

Informal street vendors are casualties.

A public-private partnership called the City Heights Community Development Corporation, together with several nonprofits, launched the initiative to increase "access to healthy and culturally appropriate food" and serve as "a business incubator for local micro-entrepreneurs," including immigrants and refugees who live in the neighborhood.

On paper, this all sounds great.

But just a few blocks outside the gates, informal street vendors – who have long sold goods such as fruit, tamales and ice cream to residents who can't easily access supermarkets – now face heightened harassment. They've become causalities in a citywide crackdown on sidewalk vending spurred by complaints from business owners and residents in more affluent areas.

This isn't just happening in San Diego. The same tensions have been playing out in rapidly gentrifying areas like Los Angeles' Boyle Heights neighborhood, Chicago's Pilsen neighborhood, New York's Queens borough and East Austin, Texas.

In all of these places, because "ethnic," "authentic" and "exotic" foods are seen as cultural assets, they've become magnets for development.

Food vendor at outdoor international marketplace called Fair@44.

Fairat44 via Instagram

A call for food justice

Cities and neighborhoods have long sought to attract educated and affluent residents – people whom sociologist Richard Florida dubbed "the creative class." The thinking goes that these newcomers will spend their dollars and presumably contribute to economic growth and job creation.

Food, it seems, has become the perfect lure.

It's uncontroversial and has broad appeal. It taps into the American Dream and appeals to the multicultural values of many educated, wealthy foodies. Small food businesses, with their relatively low cost of entry, have been a cornerstone of ethnic entrepreneurship in American cities. And initiatives like farmers markets and street fairs don't require much in the way of public investment; instead, they rely on entrepreneurs and community-based organizations to do the heavy lifting.

In City Heights, the Community Development Corporation hosted its first annual City Heights Street Food Festival in 2019 to "get people together around table and food stalls to celebrate another year of community building." Other recent events have included African Restaurant Week, Dia de Los Muertos, New Year Lunar Festival, Soul Food Fest and Brazilian Carnival, all of which rely on food and drink to attract visitors and support local businesses.

Meanwhile, initiatives such as the New Roots Community Farm and the City Heights Farmers' Market have been launched by nonprofits with philanthropic support in the name of "food justice," with the goal of reducing racial disparities in access to healthy food and empowering residents – projects that are particularly appealing to highly educated people who value diversity and democracy.

Upending an existing foodscape

In media coverage of changing foodscapes in low-income neighborhoods like City Heights, you'll rarely find any complaints.

San Diego Magazine's neighborhood guide for City Heights, for example, emphasizes its "claim to authentic international eats, along with live music venues, craft beer, coffee, and outdoor fun." It recommends several ethnic restaurants and warns readers not to be fooled by appearances.

Longtime residents find themselves forced to compete against the "urban food machine"

But that doesn't mean objections don't exist.

Many longtime residents and small-business owners – mostly people of color and immigrants – have, for decades, lived, worked and struggled to feed their families in these neighborhoods. To do so, they've run convenience stores, opened ethnic restaurants, sold food in parks and alleys and created spaces to grow their own food.

All represent strategies to meet community needs in a place mostly ignored by mainstream retailers.

So what happens when new competitors come to town?

Food vendor at outdoor international marketplace called Fair@44.

Fairat44 via Instagram

Starting at a disadvantage

As I document in my book, these ethnic food businesses, because of a lack of financial and technical support, often struggle to compete with new enterprises that feature fresh façades, celebrity chefs, flashy marketing, bogus claims of authenticity and disproportionate media attention. Furthermore, following the arrival of more-affluent residents, existing ones find it increasingly difficult to stay.

My analysis of real estate ads for properties listed in City Heights and other gentrifying San Diego neighborhoods found that access to restaurants, cafés, farmers markets and outdoor dining is a common selling point. The listings I studied from 2019 often enticed potential buyers with lines like "shop at the local farmers' market," "join food truck festivals" and "participate in community food drives!"

San Diego Magazine's home buyer guide for the same year identified City Heights as an "up-and-coming neighborhood," attributing its appeal to its diverse population and eclectic "culinary landscape," including several restaurants and Fair@44.

When I see that City Heights' home prices rose 58% over the past three years, I'm not surprised.

Going up against the urban food machine

Longtime residents find themselves forced to compete against what I call the "urban food machine," a play on sociologist Harvey Molotch's "urban growth machine" – a term he coined more than 50 years ago to explain how cities were being shaped by a loose coalition of powerful elites who sought to profit off urban growth.

I argue that investors and developers use food as a tool for achieving the same ends.

When their work is done, what's left is a rather insipid and tasteless neighborhood, where foodscapes become more of a marketable mishmash of cultures than an ethnic enclave that's evolved organically to meet the needs of residents. The distinctions of time and place start to blur: An "ethnic food district" in San Diego looks no different than one in Chicago or Austin.

Meanwhile, the routines and rhythms of everyday life have changed so much that longtime residents no longer feel like they belong. Their stories and culture reduced to a selling point, they're forced to either recede to the shadows or leave altogether.

It's hard to see how that's a form of inclusion or empowerment.The Conversation


Pascale Joassart-Marcelli is a Professor of Geography and Director, Urban Studies and Food Studies Programs at San Diego State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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