In the Lab with Keanu Reeves| From Commonwealth | By Chris Berdik, Video by Devin Hahn
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"Yeah, yeah, we're all running. OK, we're doing a lot of damage," he says, as if he's seen it all before. Actually, he has — several dozen times, and all in the name of science.
This particular maritime disaster is a scene from Speed 2: Cruise Control, one of the action flicks that features prominently in Cinema Physica, an introductory physics course for nonscience majors. Every week, Cohen's students watch movies such as Unbreakable, The Sixth Sense, and Armageddon, and use class discussions and labs to examine the basic physics driving the high-octane scenes.
"The subtitle of this course should be Bruce Willis Saves the World," Cohen tells students with a laugh. The purpose of analyzing all the explosions and heroics, he explains, is to give humanities majors a truer sense of what science is — a quest for discovery rather than for memorized formulas and precise answers.
"When you do an experiment, you don't know what the answer is going to be," he says. "And because we don't know whether the movies actually obey the laws of physics, they are our experiments. They are our laboratories."
Cohen uses The Abyss to discuss fluids and pressure, for instance, and X-Men to talk about electricity and magnetism. Last fall, after the class watched The Matrix scene where Morpheus tells Neo that the machines behind the matrix want to turn humans into nine-volt batteries, Cohen talked about the physics of batteries and whether humans would really be nine-volt — or much larger — batteries, leaving aside the movie's more existential questions.
Illustration by Eric Palma
"We didn't much go into the idea of whether we are all just pixels in a digital universe," says Adrian Coyne (CAS'11).
After watching the Speed 2 clip where the ship plows ashore and passengers are ejected through the windows, Cohen asks the class to calculate the ship's deceleration as it comes to a stop exactly one ship's length from where it first hit the pier.
When one student suggests using an equation, Cohen pounces. "Don't say equation," he says. "I never want to hear the word equation in this class. I hate equations."
He encourages students not to get hung up on exact answers when estimates will do. In Cohen's class, a few percentage points of error don't matter; what matters is learning a quantitative technique called "dimensional analysis."
The technique, simply put, requires converting the basic dimensions and units of information that you have about a scenario — a cruise ship's change in velocity, say, and the distance it traveled — into an answer that's described with different dimensions and units — such as the ship's deceleration, which is measured as change in velocity over time squared.
The class doesn't know how long it took the ship to come to rest after hitting the pier.
But the ship's speedometer gives them the initial velocity, and some Internet searching reveals the ship's length in meters. Armed with just that information, the class uses dimensional analysis to find the cruise ship's rate of deceleration — only about 0.1 meter per second squared.
"Anybody getting ejected out of that windshield?" Cohen asks with a smirk. "That's a gentle breeze. No one would be spilling their drinks."
While the movies often play fast and loose with the laws of physics, Cohen isn't out to poke holes in Hollywood blockbusters. After all, it doesn't take a physics professor to laugh away a plan to destroy an Earth-bound, Texas-sized asteroid by planting a nuclear bomb inside of it. And besides, says Cohen, a bona fide movie buff, technical accuracy isn't what makes movies fun.
But a little physics can help. Olga Cuevas-Gomez (CAS'10), who took the course last fall, says that X-Men is one of her family's favorite movies. "Now, every time we watch it, there's a new physics concept that I try to explain to them," says Cuevas-Gomez. "They never get it, but they pretend they care."