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“Explain it like I’m 5”: Mathematics, geometry and soap bubbles were the highlights of the final session of the academic year

May 15thupdated on May 18th at 16:02

Experiments with soap films and geometric structures led the young audience to explore balance, efficiency, and shapes found in nature.

“Wow!” The exclamation echoed almost in unison in the Great Hall of Instituto Superior Técnico, Universidade de Lisboa, when a huge soap bubble slowly drifted across the room, suspended in the air for a few seconds before popping. On the morning of May 13, the final session of this academic year’s “Explain it like I’m 5” initiative allowed children in 1^st to 4^th grades to explore geometric shapes, balance, and the “mathematics of soap bubbles”.

“Why are soap bubbles round?” was the question posed by Hugo Tavares, a professor at Técnico and researcher at the Centre for Mathematical Analysis, Geometry, and Dynamical Systems (CAMGSD). Standing at the front of the audience, surrounded by geometric structures, containers of soapy water, and arches of various shapes, the researcher began by challenging the audience’s intuitions.

“If we blow a bubble in the shape of a star or a heart, will it actually take on that shape?” he asked. The children made their guesses, but the same result unfolded before their eyes: the bubbles always remained round. “When we do science, we start by imagining possibilities, experimenting, and observing what actually happens”, the researcher explained.

The answer led the audience to one of the classic problems of geometry, associated with the legend of Princess Dido. “If we have the same amount of wall, what shape allows for the protection of the largest possible city?” he asked once more. Amid quick answers of “squares,” “triangles,” and “rectangles,” the conclusion eventually emerged from the audience: “the circle is the best shape”.

“The search for the smallest ‘wrapping’ explains the shape of soap bubbles”, stated the mathematician. “Soap [in contact with water] behaves like an elastic surface that tries to occupy as little space as possible”. He added that in nature, shapes tend to organise themselves in a way that expends the least energy. “The sphere emerges because it is the shape that can hold the most air using the least surface area”.

But soap bubbles weren’t the only example. When two parallel rings were dipped into the solution, a curved, translucent film formed between them, described as resembling a “vase”. “This shape is called a catenoid”, explained Hugo Tavares, as the surface undulated before the audience. “Mathematics allows us to describe and predict all possible shapes and connections of soap films”.

“A scientist’s job is to try to build models that explain what we observe in the world around us”

Throughout the demonstration, questions came pouring in. “Why do soap bubbles have colours?” asked a student. “And why are they so fragile?” asked another. Hugo Tavares explained that the colours “result from the way light interferes with the very thin layers of the soap film”, while the fragility of these structures is “due to their reduced thickness and the delicate balance” that keeps them stable.

One of the most surprising moments was a cube placed in the soapy water solution. When the researcher removed it, thin films automatically rearranged themselves inside the structure, creating unexpected geometric divisions. From the front rows, several children craned their necks to watch the transparent surfaces emerging inside the cube. “In nature, many shapes appear because they represent more stable solutions”, he noted.

As the experiments revealed similar patterns between soap films and other shapes found in nature, questions continued to arise from the audience. “Why don’t bees make triangles?” someone asked. The question opened the door to another example of “geometric efficiency”. “Bees use hexagons because they can store more honey while using less wax. Just as with soap bubbles, nature also finds efficient solutions”, explained Hugo Tavares.

At the end of the session, the children quickly left their seats to experiment with the structures immersed in soap. Amid giant bubbles, soap films that warped at the touch, and attempts to create multiple bubbles at once, various discoveries were made. Some children compared different shapes, others tested movements with the metal hoops, while others watched closely to see how long a soap film could hold before disappearing.

As the last soap bubbles faded away, Hugo Tavares left the audience with one final “homework” assignment. “Look closely at nature. There is mathematics in far more places than we imagine”, he challenged them. “A scientist’s job is to try to build models that explain what we observe in the world around us”.

Photo gallery.

This edition of the “Explain it like I’m 5” initiative featured eight sessions dedicated to different research areas conducted at Técnico. The project will return in October 2026 with new topics aimed at younger audiences.

Previous talks:

8 October 2025, 10 a.m. – “How does a satellite work?” – João Paulo Monteiro (ISR-Lisboa)

News published on the Técnico website: “How does a satellite work?”: Técnico opened its doors to the curiosity of young children

12 November 2025, 10 a.m. – “How does a laboratory that fits in the palm of your hand work?” – Vânia Silvério (INESC-MN)

News published on the Técnico website: “A laboratory that fits in the palm of your hand: children discover micro-scale science at Técnico”

10 December 2025, 10 a.m. – “What happens to toilet water?” – Ricardo Santos (LAIST)

News published on the Técnico website: Children explore the invisible journey of water during the third science talk “Explain it like I’m 5”

4 January 2026, 10 a.m. – “What is radiation used for?” – Joana Madureira (C2TN)

News published on the Técnico website: “Explain it like I’m 5” kicked off in 2026 with a session dedicated to radiation (which ‘we [human beings] also transmit’)

6 February 2026, 10 a.m. – “Did you know that there are cities where every drop of water counts… and others where every drop is wasted?” – Filipa Ferreira (CERIS)

News published on the Técnico website: “Every drop has a path”: a journey through the water cycle explained to children at Técnico

18 March 2026, 10 a.m. – “Where do the things we use to make other things come from?” – Amélia Dionísio (CERENA)