Children and teenagers have been playing with science since the 19th century, and for decades, kits of scientific experiments or miniature machines and equipment were coveted items for children's birthdays and Christmas.[I]These toys sometimes resurface in the tangle of fond memories of people who never stopped playing and ended up as professionals in scientific fields.[ii].
The fundamental instruments used in the so-called scientific revolution of the 17th century: the telescope and the microscope.[iii]They appear in plastic versions in some toy stores, while at the forefront of science, increasingly sophisticated versions are used, bearing little resemblance to those of centuries ago. But would the reverse be possible: toys that transform into instruments of science? And not in that now distant era, but in more recent times or even today?
Two examples suggest this possibility, which is curious but far from being a proposed methodological approach. The first goes back to the early days of quantum mechanics and computers, a century ago, with a technically sophisticated toy. The second revisits a popular and inexpensive toy.
The famous Schrödinger equation, from early 1926, describes the behavior of the quantum world. The first test, presented by Erwin Schrödinger, was to solve it for the hydrogen atom, reproducing the energy levels of the atom's single electron, obtained by Niels Bohr thirteen years earlier. But the new equation went further: it showed how this electron, which is no longer a small ball, was distributed throughout the atom according to its energy. This famous partial differential equation, in principle, applies to the entire microscopic world. However, the hydrogen atom has only one electron, and the equation in this case has an exact solution, obtained only with pencil and paper. And what about other atoms with multiple electrons, not to mention molecules? These are the "many-body problems," without an exact solution, only an approximate one, and worse: solving a single such problem with only paper and pencil would take years.
What was needed then was a machine to solve these equations more quickly: the differential analyzer, a mechanical equivalent of the computers that came later. Its operation was based on sets of discs and wheels coupled by shafts, gears, and torque amplifiers, which performed what in mathematics is called integration. It's the same principle as the differentials in automobiles. The first differential analyzer for practical use was built at the Massachusetts Institute of Technology (the famous MIT) by Harold Locke Hazen and Vannevar Bush in the late 1920s and 1931. Finally, a machine to solve differential equations!
But what about the Schrödinger equation? A young English physicist at the time, Douglas Hartree, proposed a procedure in 1927 to solve this equation, taking into account the interaction between electrons in an atom with several of them. It was called the self-consistent field method. But it was tedious to calculate, because you start with an initial "guess," and the result obtained becomes the "guess" of a new calculation, whose result is a new "guess." Until, after many steps, the result is equal to the last "guess," and that's it, that was the final result. A brilliant idea, but how to implement it? Hartree brought the idea of the MIT analyzer to the United Kingdom and, together with student Edward Porter, built the "first differential analyzer outside the United States" to perform the calculations of his method. And that's where the toy came in: Hartree's equipment was built with parts from Meccano, a game with metal components to assemble miniature cars, trains, cranes, and machines. It was so successful that other computers were built using the same toy.
The whole story was detailed by Thomas Ritchie in his 2019 doctoral thesis: “Object Identity: Deconstructing the Hartree Differential Analyzer and Reconstructing a Meccano Analog Computer”.[iv]Prior to this thesis, Tim Robinson had reconstructed Hartree's computer exactly as it had been originally built.[v]This could be an interesting idea as an interdisciplinary science teaching project, and if Meccano parts are unavailable, a 3D printer could be used.
This was a complex problem solved with a sophisticated toy. But what to do with a simple spinning top? The popular toy, present in various cultures, is what the girl in the illustration has in her hands: a disc with string pierced through two holes spins merrily when the twisted string is pulled, stretching and then twisting again continuously.
Manu Prakash, a bioengineer at Stanford University, used the whirling disc to solve a crucial problem: building super-cheap, hand-operated centrifuges (without electricity) for analyzing blood samples in isolated communities. The bioengineer and his students studied the physics of this device and managed to get it to reach over 100 rotations per minute, enough to separate plasma from the rest of the blood in a minute and a half and isolate malaria parasites in 15 minutes. The blood sample, collected from a fingertip, is placed in a capillary tube that is attached along the radius of the disc, and voilà: diagnosis from making the whirling disc spin.
The article presenting the instrument, its operating principle, and tests with blood samples was published in 2016, with a title that summarizes its purpose: "Ultra-low-cost hand-operated paper centrifuge".[vi]The videos and materials available demonstrate the ideas and concepts without the dryness of academic text.[vii].
Before his paper centrifuge, Manu Prakash developed the foldscope (“dobrascope”): a very low-cost microscope made of folded paper, like origami, and a simple lens. He distributed thousands of them around the world and encouraged the sharing of different observations of fungi, parasites, and cells on a portal.[viii] featuring a gallery of images and illustrations of the scientific origami assembly.
Manu Prakash dedicates himself to the "frugal science" or "recreational biology" movement. One of his projects reinterprets a popular toy, while another revives 17th-century science in the 21st century. After all, the "dobrascope" is basically Antony van Leeuwenhoek's microscope.[ix], whose observations he shared through letters, since the internet did not yet exist.
Science, in addition to being interdisciplinary, can also be intersemiotic.
This text does not necessarily reflect the opinion of Unicamp.
[I] Today's article is somewhat anachronistic.but it recaptures the charm of science toys.
[ii] https://jornal.unicamp.br/video/2026/02/02/mente-aberta-ao-novo-e-combustivel-para-o-avanco-da-ciencia/
[iii] SCHULZ, Peter. “Part 4 – The Instruments of Science”, in Science in action – who does it, how it's done, where it's done, Faccioli Editorial, 2025
[iv] Object Identity: Deconstructing the 'Hartree Differential Analyser' and Reconstructing a Meccano Analogue Computer
[v] A summary report can be read. in Tim Robinson's articlesn, a Meccano fan and mentioned in Ritchie's thesis.
There are several videos on YouTube showing this mechanical computer in operation, the link is to Tim Robinson's.
[vi] Hand-powered ultralow-cost paper centrifuge.
[vii] https://www.ted.com/talks/manu_prakash_lifesaving_scientific_tools_made_of_paper
