Physics on display

Hundreds of regional junior high and high school students visited Penn’s campus in early January to beat the winter blues—and reds—by watching physics demonstrations about lights and waves.

a metal tube with a line of flames coming out of the top and a blurred person posing in the background
A Rubens’ tube, which uses pressurized propane to bring sound waves to life with fire, was one of several demonstrations from the lights and waves winter physics show.

On Jan. 14 and 15, more than 850 students from the Philadelphia area attended one of four Winter Physics shows hosted by Penn’s Department of Physics & Astronomy. The show focused on the topic of light and waves, with demonstrations led by Peter Harnish, Mary Marcopul, and Bill Berner.

Harnish has been running the undergraduate physics labs for the past four years. Marcopul will be taking over the management of the physics demonstration lab from Berner, who founded the show, and is retiring after more than 20 years performing demonstrations that give students a look into the world of physics. 

harnish, berner, and marcopul laugh together while standing in a room full of tools and equipment
Harnish, Berner, and Marcopul  (pictured in the physics demonstration lab) took turns leading a series of demonstrations during the two-hour show.

Berner, Harnish, and Marcopul took turns conducting a series of physics demonstrations during the first half of the show. Harnish, who kicked things off, said, “This show is not meant to teach you a semester’s worth of physics in two hours. The goal is that when you’re back in your classroom, you’ll be able to understand what happens next because you will have seen it happen here at this show.”

berner motions with his hands in front of a wave-generating machine as he explains a physics concept
Berner founded the winter physics show and is retiring after more than 20 years of performing demonstrations. He has played an instrumental role in providing regional students with a glimpse into the world of physics.

This year’s show posed simple questions such as “What does it mean to see?” and then, using star showers and funhouse-mirror illusions, showed how light travels. The science of focal points was illustrated to dramatic effect using two parabolic mirrors, a heat lamp, and a piece of flash paper. With the heat generated by the lamp on one side of the room, Marcopul, who previously taught physics at Owen J. Roberts High School, and has more 18 years of teaching experience, ignited a piece of paper held more than a yard away using the energy transferred from one mirror’s focal point to the other.

It is visual experiments like this that Scott Taylor, a science teacher from PS Du Pont Middle School, relies on when he and his students return to the classroom. Seventy of his students made the trip from Wilmington, Del., just to see the show.

His eighth-grade gifted science class will soon be covering the topic of electromagnetic waves, and he said that this show was well-timed to help teach these complicated concepts. “I can bring these demonstrations up when I am teaching to help them make a connection about what we do in class. It’s more powerful for them than just looking at a book. It’s great that Penn does this, and both I and my students really enjoy the visual nature of these shows,” said Taylor.

After a brief intermission, the focus shifted from lights and optics toward wave phenomena. Visual and acoustic demonstrations, including a wave machine, a rainbow-producing spherical lens, an analog noise canceling device, and silencing a bell in a vacuum, were used to explain fundamental concepts in physics such as frequency, wave propagation, and interference.

The show ended with demonstrations of a Rubens’ tube. This closed metal tube contains a speaker at one end and has a series of holes running along the top. Propane gas is pumped into the tube and differences in pressure are used to bring the images of the sound waves to life with flame. Higher tones produce more waves, which Harnish demonstrated by changing the pitch of the input sound to form additional undulations along the tube. 

Harnish even got some audience members singing along, when he played Adele’s “Hello” and  “Rolling in the Deep” through the Rubens’ tube. The music created perfectly shaped sine waves along the tube that pulsated in time with the beat of the song. Harnish commented that Adele’s song “looks” so impressive because she is one of the few artists with long-enough sustained notes that form perfect sine waves. 

harnish and marcopul talk to each other while surrounded by equipment and tools
Harnish runs undergraduate physics labs while Marcopul will be taking over the management of the physics demonstration lab from Berner. Marcopul and Harnish will continue the winter physics show tradition of using visual and impactful demonstrations to illustrate key concepts in physics to regional junior high and high school students. 

From his time working as Berner’s assistant, Harnish has been a part of each of the physics shows in the three-year rotation: mechanics, electricity and magnetism, and lights and waves. He admitted that he was nervous about leading the show, in part because he didn’t have 20 years of experience, or a complete “script” in his head like his predecessor. But after the Monday afternoon show Harnish seemed pleased with how things went, even with a few imperfect transitions between demos. He said he prefers it that way. 

“It’s not set up to be a magic show,” Harnish said. “It still has parts that are rough around the edges, which is how it should be. That’s what this show is all about; it’s science, not magic.”