Opinion

One of the challenges of science communication is to create an unexpected encounter between the average person and science—any excuse is a good one to talk about it. But could we also find such an encounter at a festival as popular as San Fermín?

Science in White and Red
That was the challenge we set for ourselves at theUniversity of Navarra Science Museum, in collaboration with other organizations, including the Spanish Foundation for Science and Technology (FECYT) of the Ministry of Science, Innovation, and Universities: to explain, through texts and detailed infographics, the physics, biology, chemistry, history, and archaeology behind Pamplona’s famous festivities, which begin on July 6. At what height does the chupinazo go off? How many people can fit in Pamplona’s Town Hall Square on that day? What was Pompelo, the Roman city, like during the time of San Fermín? How do you dance with a giant so it doesn’t tip over? Is the bull run faster than it used to be?…

The Chemistry and Physics of the Chupinazo
The San Fermínchupinazois not only the symbolic start of the festivities, but also a chemistry and physics experiment right in the Town Hall Square. The rocket contains about 25 grams of black powder, a mixture of potassium nitrate (75%), charcoal (15%), and sulfur (10%). When ignited, the sulfur and charcoal burn rapidly, using the oxygen provided by the potassium nitrate. This combustion produces a large amount of gases which, as they are expelled downward, generate—according to Newton’s law of action and reaction—the force that propels the rocket upward until it reaches an altitude of between 500 and 1,000 meters. At the moment of detonation, it emits a sound of 133 decibels, similar to the noise of an airplane taking off.

At that moment, more than 12,000 people can gather in a small square measuring about 2,500 m².Studieshave shown that what appears to be a chaotic, jostling crowd actually behaves like a collective system, similar to a fluid. These are human tides moving in a self-organized, synchronized manner, with oscillations every 18 seconds. Understanding the physics of large gatherings of people can improve safety at mass events.

Science in Motion: From the San Fermín Bull Runs to the Dance of the Giants
The bulls in the San Fermín bull runs, which can weigh over 600 kilos, are getting faster and faster: they can reach speeds of around 20–25 km/h, while the average human reaches about 15–20 km/h.

Since 2005, the bull run route has been treated with a chemical anti-slip solution that reacts with the silica component of the pavement. This creates an effect similar to a “suction cup,” which improves traction for the bulls’ hooves and reduces the risk of falls. As a result, the runs have become increasingly faster:in 2015, the record was broken with a time of 2 minutes and 15 seconds.

The San Fermín giantsseem to move with great ease, but keeping a figure over four meters tall and weighing nearly 60 kilos in balance is not just a matter of strength, but of coordination and balance. The challenge is to keep the center of gravity within the base of support. If the vertical line connecting the center of gravity to the ground falls outside the area where the feet are planted, the giant can tip over. To prevent this, the bearers spread their feet apart to increase stability and bend their knees when they need to slow down or regain their balance.

The Five Senses of the Bull
Bulls do not have horns, but rather antlers, since the two differ in their composition, growth, and function. Antlers are found primarily in bovids—such as cows, goats, and antelopes—and consist of a permanent bony core covered by a keratin sheath. They do not branch, do not shed, and continue to grow throughout the animal’s life.

In contrast, antlers are characteristic of cervids—such as deer, reindeer, and moose—and are composed entirely of bone. They grow annually, branch out, and are temporarily covered by a vascularized skin called velvet. After the mating season, the antlers shed, and the cycle begins anew. These differences reflect evolutionary adaptations to specific lifestyles and behaviors.

Thefighting bullhas evolved to detect predators and threats in open environments. As a result, these animals have a wider field of vision, although they are farsighted and have a blind spot. They have a high proportion of rods in their retinas (high sensitivity to movement), but only two types of cones for blue and green-yellow (they see red and orange as grayish or muted tones). One of the most widespread myths is the idea that the bull charges because it is attracted to the color red, when in reality it is movement that attracts it.

Fireworks: Pure Chemistry
Fireworksare now a staple of all popular festivals, and their colors are due to the metal salts they contain. Heating the gunpowder excites the electrons in these salts, causing them to “jump” to a higher energy level. Since this state is unstable, the electrons immediately return to their original state, releasing the excess energy in the form of light of a specific vivid color. Thus, red is caused by strontium salts, green by barium, blue by copper, yellow by sodium, and orange by calcium.

A Trip to Pompelo
According to tradition, Fermín was the son of a Roman senator from the city of Pompelo named Firmo. But what was Pamplona like in the 3rd century, the era in which the city’s first bishop lived?

Pompelo, founded by Pompey in 72 B.C.E., was organized into terraced levels.Archaeological evidencesuggests that it consisted of a medium-sized urban center, covering an area of around 20 hectares and with a population of approximately 6,000 inhabitants. The forum, the heart of civic, administrative, and religious life, would have occupied a central and dominant position. The thermae (public baths and leisure centers) would have formed part of the forum’s monumental landscape, reinforcing its role as the nerve center of urban life in a typical Roman city.

This article was originally published in The Conversation. Read the original.