Standing on a skateboard with a medicine ball in his hand, Zach Tobin asks what will happen if he throws the ball. He does so and proceeds to glide shakily in the opposition direction. "Equal and opposite forces, right?" he says. The scene might seem like something you would see on TikTok, but in fact is one of many physics demos that Tobin has catalogued as part of his job at Caltech. The demos cover many basic principles such as Newton's laws of motion, the relationship between electrical currents and magnetic fields, and the conductance of electricity by air. The demos also include props such as stuffed monkeys, lava lamps, and tubes of flames.
"Part of my job is playing with fun toys," he jokes. "But what I like about my work is the breadth of topics I get to cover, from electromagnetism to quantum mechanics, and more."
Tobin has been a physics lecture hall manager at Caltech since 2017. Half of the job involves managing the Feynman Lecture Hall, where introductory physics courses are taught. This includes maintaining the hall's equipment, scheduling, and other logistics. The other half of the job entails managing Caltech's collection of physics demos and related gadgetry, some of which date back nearly 130 years.
"The oldest experiment in the collection, called the Peltier-Seebeck device, is from 1895, before Caltech was even called Caltech," he says. The device is a thermoelectrical generator that couples the voltage in different objects to differences in temperature.
The collection includes more than 250 demos, more than 200 of which are catalogued on video and available online. Tobin notes he began to put even more demos on video due to the COVID-19 pandemic and resulting shift to online learning.
"It's great to have somebody like Zach on campus who has such an extensive knowledge of physics demos for students," says Brad Filippone, Caltech's Francis L. Moseley professor of physics.
Sometimes Tobin will help develop new demos or update existing ones, while others stand the test of time.
"There is a whole spectrum of different styles of demos, where some are future proof, some require updating, and some just degrade over time," he says.
Tobin said several professors asked him a few years ago to develop a so-called Rubens' tube demo, which illustrates the relationship between sound waves and pressure. Basically, a tube with holes is filled with propane and lit on fire. The result looks like "a bunch of candles in a tube," says Tobin. Sounds and music passing through the interior of the tube cause the flames to rhythmically undulate, which you can see in the demo Tobin developed and posted online.
More recently, Tobin says a few professors, including Filippone, have requested a well-known quantum physics demo called the single photon interference experiment. In this demonstration, a single photon is sent through two slits and produces an interference wave pattern even though only one photon is used. How can that be? This has to do with a physics concept known as wave-particle duality. As a single photon moves through the apparatus, it behaves like a wave, extended in space and passing through both slits. When detected on the other side of the slits, it then behaves like a well-localized particle.
Tobin says Filippone is helping him put together the demo, but that it is technically complicated to build for several reasons, including the fact that the laser beams used to produce the photons need to be carefully adjusted to send out only single photons.
Tobin's career path may have stemmed from inspiration he received in college. He recalls the time a teacher placed a cinder block on their hand and "started hammering it to death." Luckily, the block was massive enough to absorb all the energy and not cause damage to the teacher's hand, as you can see here in a similar demo by Tobin. That same teacher also ate chalk, he recalls.
Later, Tobin went to Caltech for graduate school and studied in the lab of Caltech Professor of Applied Physics Paul Bellan. He left after earning a master's degree in physics.
"I had built a plasma gun, and when I was finished, I realized that what I really liked was operating the gun, but I was not as interested in the frequencies of the various atoms in it," he says. "I started to realize the difference between a scientist and an engineer."
Tobin then worked at Pasadena High School, where he developed computer and math classes, and taught Android app development and robotics. But he said that job "wasn't really for me" either.
Now, Tobin is happy to have found his way back to Caltech. Outside of his job responsibilities, he also builds props for Caltech theater productions. He helped create a giant, carnivorous plant for a production of Little Shop of Horrors, and even made Klingon weapons called bat'leths for a raucous production of Boldly Go, a musical parody based on the television show Star Trek.
Theater, he says, is not that different from science demos. "You need something interesting to look at or most people aren't going to care."