Engineering: Believe it!

Did you catch Ursula Gibson '76's "Believe it or Not" cartoon about electrons and beaches? Well, believe it or not, Ripley's got the factoid almost right. "The hairdryer would have to be direct current, not alternating current," the Thayer engineering prof says. And the beach would only be a centimeter or two thick, "just enough to wiggle your toes in."

But what's an engineering professor doing in Ripley's anyway? Gibson says she merely responded to then-Thayer dean Elsa Garmire's suggestion that submitting engineering esoterica to Ripley's would bring the Thayer School into the public eye. Gibson dipped into her ready supply of calculations that she uses to "get people to wrap their minds around big numbers" and to spark up her classes. "People have short attention spans, so ideally, one should try to give students problems to interact with a couple of times each lecture," she says.

She'll interrupt a lecture to ask how many piano tuners there are in Chicago. "The initial response is, 'I don't know.' Then they start estimating the population of Chicago, the percentage of people who own pianos, the number of tunings done in a year, the number of tunings a person can do in a day. They come out with an estimate—and the knowledge that the inaccessible can be approached."

Take jelly doughnuts, says Gibson, turning to another classroom example. How many times would a person have to walk from the river to Thayer to burn off a jelly doughnut if the body were 100 percent efficient? "If one does the calculation based on the physics definition of work performed, and assumes that one regains no energy going downhill (otherwise it takes an infinite number of trips), 250 Calories = 250,000 calories = one million joules. Assuming a 100-foot elevation change and a weight of 140 lbs., it would take 20,000 joules per trip, or about 50 times up the hill to work off the jelly doughnut." But we're not efficient, says Gibson—and that's the point. How many trips does it really take to work off the doughnut? A merciful four or five.

"Note well," the professor adds, "these numbers are approximate!"