The Balancing of Bicycles

This month’s Photos of the Month was inspired by a recent episode of the podcast Unexplainable. (Shout out to the Unexplainable crew, who have used resources from our library & archives in previous episodes and provided some of the references used in this blog post!)

In this 30-minute episode, the hosts Noam Hassenfeld, Meradith Hoddinott, and Brian Resnick quiz guest Avery Trufelman on three scientific mysteries. Avery has to guess which mystery has recently been solved, and which two mysteries remain unsolved. The mysteries in question include:

1. We do not understand how air turbulence in our atmosphere works.
2. We do not understand why the surface of ice is slippery.
3. We do not understand how bikes self stabilize.

Now, I won’t spoil the entire episode for you, but I can tell you that one of the UNEXPLAINED mysteries of science is item number 3 - we can’t figure out why bicycles balance so well. This phenomena, known as self stability, has evaded scientists for centuries.

In 1970, David Jones’ Physics Today article and more recently J.D.G. Kooijman, J.p. Meijaard, Jim M. Papadopoulos, Andy Ruina, and A.L. Schwab’s 2011 Science paper formally debunked the leading theories of both the gyroscopic effect and caster effects as the single rationales for bicycle balance. You can see an example of the 2011 research group's bicycle that shows self stabilization even when the caster effect is negated here.

The reason why bicycles self-stabilize? Well… for now it’s ~unexplained~ (or at least very complicated) and the scientific community will have to keep researching.

Please enjoy this set of Photos of the Month, showing a bunch of scientists from the past who were too busy riding bikes to investigate the dynamics of the bicycle itself!

Overhauser Albert G1 Image Credit: AIP Emilio Segrè Visual Archives, Overhauser Collection, Gift of Dr. Overhauser

Albert Overhauser (yes, that Overhauser) and his family demonstrate that biking is for kids and adults of all ages!

Parker Robert B1 Image Credit: AIP Emilio Segrè Visual Archives, American Geophysical Union (AGU) Collection

Geophysicist Robert L. Parker is, in his own words, a “Serious recreational road cyclist.” He’s shown here with his road bike.

Wood Robert Williams F4 Image Credit: AIP Emilio Segrè Visual Archives

This image, credited to Robert Williams Wood, was a mystery to me, until I got my hands on a copy of William Seabrook’s Doctor Wood: Modern Wizard of the Laboratory. I’ll let Seabrook introduce what is happening here: 

In the summer of 1909 Mars was in opposition, and all the astronomers were on tiptoe. Wood took out the six-inch lens of his big spectroscope at East Hampton and mounted it on a block of cement on the lawn in front of his laboratory door. A silvered mirror reflected the light of the red planet through the lens and thence to an eyepiece forty feet away, at the back of the dark laboratory, where he viewed the magnified image of the planet while lying comfortably on the floor on an old mattress. During this same summer he resumed his experiments on photographing the moon in ultraviolet light…

Wood then took this spectroscope mounted on cement to a new level, as described in this 1910 paper: “The preliminary experiments were made at my summer laboratory… with an improvised instrument made out of odds and ends…” He attached a 6-foot photographic telescope made with a quartz lens to an iron stove-pipe with a photographic plate holder on one end, and then attached all of that to a 5-foot astronomical telescope that could follow the moon over the three minutes needed to expose the photograph. “Both were attached to an equatorial mounting made of an old bicycle frame embedded in a block of cement, the steering axis pointing to the pole star. A slow motion enabled me to make exposures of several minutes if necessary.”

You can view the photographs of the moon and results of this labor in the above-mentioned paper, and if you’d like to make your own, luckily Dr. Wood published some instructions here! For more information on Wood, who was quite the character, I highly recommend Joanna Behrman's blog post from last April: Pipes, Poems, and Physics: The Life of R.W. Wood.

Curie Pierre C7 Image Credit: Photo from Laboratoire Curie, Institut de Physique Nucleaire, courtesy AIP Emilio Segrè Visual Archives

Pierre and Marie Curie in Sceaux, outside Paris, in 1895 with bicycles they purchased with gifts from their recent wedding. The Curies often enjoyed long bike rides together.

Weisskopf Victor C6 Image Credit: AIP Emilio Segrè Visual Archives, Physics Today Collection, Gift of Jost Lemmerich

Victor Weisskopf, Maria Goeppert Mayer, and Max Born bike riding together. Although the date is unknown, it’s likely that this photograph was taken in Göttingen while Weisskopf and Mayer were students under Max Born’s guidance.

Bethe Hans C14 Image Credit: Copyright Cornell University

Hans Bethe and Boyce McDaniel take a spin around Cornell’s Wilson Synchrotron Lab, in 1968, proving that Cornell’s scientists were so dedicated to accelerating that they even did it in their spare time - just on bicycles!

References and further reading

• Transcript of Unexplainable episode: https://docs.google.com/document/d/1fhJU0hxqg-vijDXNS5ilulivMAJr6B-OwsbHfWeQIA0/edit 
• Whipple, F. J. W., The stability of the motion of a bicycle, The Quarterly journal of pure and applied mathematics, Volume 30, 1899, Page 312-348; https://babel.hathitrust.org/cgi/pt?id=hvd.32044102924578&view=2up&seq=336
• Jones, David E. H., The stability of the bicycle, Physics Today, Volume 23, Issue 4, April 1970, Page 34; https://doi.org/10.1063/1.3022064
• Kooijman, J. D. G., et al., A bicycle can be self-stable without gyroscopic or caster effects, Science, Volume 332, Issue 6027, April 15, 2011, Pages 339-342; https://www.science.org/doi/10.1126/science.1201959
• Borrell, Brendan, The bicycle problem that nearly broke mathematics, Nature, Volume 535, July 20, 2016, Pages 338-341; https://www.nature.com/articles/535338a
• Wood, R. W., An Easily-Constructed Equatorial Mount for Small Telescopes, English Mechanic and World of Science: No. 2329, November 12, 1909, Pages 348-349; https://hdl.handle.net/2027/uc1.c2631618?urlappend=%3Bseq=369%3Bownerid=13510798902948384-397 
• Wood, R. W., The Moon in Ultra-violet Light: Spectro-selenography, Monthly Notices of the Royal Astronomical Society, Volume 70, Issue 3, January 1910, Pages 226–228; https://doi.org/10.1093/mnras/70.3.226
• Behrman, Joanna, Pipes, Poems, and Physics: The Life of R. W. Wood, Ex Libris Universum, April 27, 2022; https://www.aip.org/history-programs/niels-bohr-library/ex-libris-unive…