# Simanaitis Says

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# BERNOULLI’S  JAALI

ARCHITECTS OF THE TAJ MAHAL, Formula One designers, and cricket bowlers have all been inspired by Daniel Bernoulli. Here are tidbits on these gleaned from BBC as well as my usual Internet sleuthing.

Bernoulli, born in The Netherlands, came from a family of mathematicians. His father Johann was one of the developers of calculus; his uncle Jacob discovered the mathematical constant e. Daniel excelled in mathematics, physics, and medicine (especially the aspects of blood flow). He lived in the era when the term “natural philosopher” described what came to be known as “scientist,” a term not used until the early 1800s.

Bernoulli’s Principle. In 1738, Bernoulli discovered that a moving liquid exchanges its specific kinetic energy for pressure, succinctly, 1/2 ρu2 + P = constant, where ρ is density of the fluid, u is its velocity, and P, its pressure.

Said another way, an increase in the speed of a flow occurs with a simultaneous decrease of its pressure.

Venturi Effect. Giovanni Battista Venturi, 18th century natural philosopher, discovered an application for Bernoulli’s Principle. Namely, the decrease in pressure of a flow’s increased velocity can be employed, for example, to suck fuel into an engine’s air intake. Or to suck a race car onto the tarmac.

Race Car Ground Effect. Formula One designers route airflow into the constricted ground clearance of a race car. Following Bernoulli’s Principle, this accelerated airflow exhibits reduced pressure—and the resulting ground force enhances grip. It’s well known, though thankfully not generally exhibited, that a speeding race car can stick to the ceiling of a tunnel. Clive Chapman, Lotus-founder Colin’s son, gives an example in this YouTube.

Kewl Buildings. BBC’s Feza Tabassum Azmi describes “How India’s Lattice Buildings Cool Without Air Con,” September 20, 2022.

Azmi explains, “The term jaali, meaning net, is used in Central and South Asia. Cut from marble or red sandstone in ornamental patterns, jaali was a distinct architectural feature in India between the 16th and 18th century. Exquisitely carved jaalis of the Taj Mahal, built in the Indian city of Agra in the mid-17th Century, create a rhythmic blend of solids and voids, concave and convex, lines and curves, light and shadows. The Hawa Mahal, or Wind Palace, built in 1799 by Rajput rulers in Jaipur, has 953 windows with lattice screens designed to let in a gentle breeze.”

Bernoulli’s Jaalis. Following Bernoulli’s Principle, a breeze accelerates through the jaalis, thus lowering its pressure. Upon exiting, its lower speed and higher pressure result in a reduction of temperature.

Azmi cites “A 2018 assessment by Batool of three-screen shading systems found that jaali outperformed both fully glazed facades and brise-soleil facades, which deflect sunlight.”

A Cricket Application. As described in Wikipedia, “During a cricket match, bowlers continually polish one side of the ball. After some time, one side is quite rough and the other is still smooth. Hence, when the ball is bowled and passes through air, the speed on one side of the ball is faster than on the other, and this results in a pressure difference between the sides; this leads to the ball rotating (“swinging”) while travelling through the air, giving advantage to the bowlers.”

Ain’t natural philosophy fascinating? ds

### 2 comments on “BERNOULLI’S  JAALI ”

1. Jack Mason
September 27, 2022

Speaking of Bernoulli, I just watched a You Tube video of the Stipa-Caproni aircraft. This stubby (and ugly) little thing would be a great candidate for your flight simulator software.

• simanaitissays
September 27, 2022

I know that aircraft and, as you say, it’s ugly. One of my few rules on GMax projects is the plane has to be something I won’t mind staring at for hours on end, while I figure out one thing or another. Alas, the Caproni doesn’t cut it. By contrast, the ducted-fan Manapare did. Thanks, but no thanks.

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