Matter Magazine: How the Physics Club Rose to Victory

By: Achyuta Rajaram

Exeter Physics Club competed in the 2021 US Invitational Young Physicists Tournament, snagging first place in astounding fashion: by 1 point! It was the third time in four years, a feat that you might have read before, either in this very newspaper or on Exeter’s website. That’s not the story that I want to tell here. Instead, I take a look at the comprehensive science used to create Physics Club’s winning solutions.

Although four problems were given, I take a look at two:

1. Lava Lamp: Edward Craven Walker and David George Smith invented the Lava Lamp in 1963, and it soon became a fad, remaining popular throughout the 1970s. Investigate, both theoretically and experimentally, the physics of lava lamps.

For Lava Lamp, we focused on the motion of particles of “oil” within the “water” of the lamp. We noticed that convection in the lamp drove all particle motion, while the temperature-density relationship spurred the bubble of wax to float and sink at specific intervals. Fourier’s law of heat conduction, a mathematical model for temperature gradients and heat conduction systems at thermal equilibrium, was an important foundation for determining the cyclic movement of the bubble of wax. As experimentation was impossible, we used data from several research papers to verify our understanding of the phenomenon. 

Pictured below the result of a simulation done on the location of the lava lamp bubble. In the words of the wise Neil Chowdhury, “I really love how lava lamps rise and fall like the stock market.”

2. Joseph Henry’s Rocking Motor: In 1831 Joseph Henry invented the first electromagnetic motor, or as he put it: “I have lately succeeded in producing motion in a little machine by a power, which, I believe, has never before been applied in mechanics—by magnetic attraction and repulsion.” Read Henry’s article and reproduce his experiment. Clearly explain how it works using Henry’s reasoning, and then using modern electromagnetic field theory. Next, design and build a solar-powered electromagnetic rocking motor optimized for pumping water in an arid rural area.

For Motor, we were unable to work in a lab, and therefore unable to create the physical motor. Instead, we focused on theory, and learned how the principles of electric fields and electromagnetism applied to the motor. Specifically, Henry initially believed that the switching polarities of the rocking motor (as it formed an electromagnet) powered its actions. Through the modern lens, however, there is a key facet missing in this explanation— the inductive nature of the centerpiece of the motor. This aspect allows for a smooth transition between polarities, meaning that the motor can move constantly without snapping between the sides, which would cause unnecessary wear and tear. In any case, the motor functions through an electromagnet that tilts from side to side, making contact with batteries that flip the polarity of the motor, resulting in its characteristic “rocking” motion.

This same type of study was done for the other two problems, and the team was well-prepared when tournament day finally arrived. Indeed, on Jan. 30, Exonians brought home victory for the Academy once again.