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Motor contest revs up physics class

Students built tiny motors to participate in a contest in freshman physics class.
Students built tiny motors to participate in a contest in freshman physics class.
Photo / Donna Coveney
JungEun Lee and Professor Walter Lewin.
JungEun Lee and Professor Walter Lewin.
Photo / Donna Coveney

The freshman physics students file into Room 26-110, gingerly holding their contraptions: palm-sized hunks of wood sprouting red wire coils and paper clips like insect feelers.

Comments fly. "Are we allowed to hold the battery? Nothing in the rules said anything about that."

"Mine got smushed. I wasn't paying attention, and I put my hand on it."

"It looks really fast because it's so small."

The most common is, "I don't know if it works!"

It is April 2, day of reckoning in the Great Motor Contest.

Professor Walter Lewin of physics, who held the same contest when he taught Physics 8.02 in 1984 and 1988, on March 1 gave each of the 500-plus kids in his introductory classes two magnets, two thumbtacks, one block of wood, two paper clips and around 2 meters of insulated copper wire. Their assignment was to build an electric motor using only these materials and a flashlight battery. Even a drop of glue would disqualify them.

The reward, Lewin said, is "hands- on experience. Doing something that is 'not the usual' (my lectures are in more than one way 'not the usual') is great for the morale of the class!"

"It brings the class closer to me and vice versa," he adds.

The builder of the fastest motor gets a "special prize." The builders of the top six motors are treated to dinner with Lewin at a local restaurant.

Not last on the list of possible motivators is one extra credit bonus point for every 100 rpm of the motor. If a motor runs 400 rpm, its creator gets four extra credit points. If it runs faster than 2,000 rpm, he or she gets 20 extra credit points: the equivalent of two homework assignments. Two homework assignments could take up to 16 hours, so the builder of a successful, fast motor reaps a big reward.


It's too warm, and the three stroboscopes measuring the speed of the students' motors are making clunking noises and sending blinding flashes of light around the room. No one seems to notice.

The students stand patiently in line, cradling their devices close to their bodies, peering at them, tinkering with them. Some use paper clips to suspend the wire coils. Some have stacked magnets; some magnets are in pieces. At least one student hollowed out his block of wood and perched the mounted coil inside.

A young woman holds up her motor. "Eighteen hundred," she says proudly. Slinging her backpack over her shoulder, she takes a cookie off a plate and leaves.

"The winner is going to be above 2,000, believe me," Lewin says. "For dinner with you, it should be," retorts one of the assistant testers at the next table.

Lewin sits at a table directly in front of a blackboard at the front of the room. Wearing a black-and-white, batik-patterned shirt over a pink-and-white striped Oxford with the sleeves rolled up, signature floppy cloth cap perched on his head, Lewin has a rubber sunny-side-up egg pinned to the front of his shirt. It looks like someone flung it at him and it stuck.

"Are there any more cookies?" he asks no one in particular. A few seconds later, a cookie appears. He maintains a running commentary as he operates the strobe. "This guy cut his magnets," he points out. "Do you know when you cut a magnet in half, perhaps you get a magnetic monopole?" he asks. (This is a joke. There is no such thing as a magnetic monopole.) "Who's next?"

Some of the motors are so delicate, they look like they might fall apart. The students prod them gently to get them started. Some blow on them. "They all need a little push to get started," Lewin says, dabbing a dot of white Liquid Paper onto the red coil of Sonam Leki Dorji's motor. At 1,550 rpm, the spinning red coil on her motor appears completely motionless. You can see only one white dot--at the incorrect rpm, there is a double image.

"Look at that," Lewin admires. "That's a nice motor, very stable."

"OK, the motor appears to stand still at 550, so we double the strobe frequency to 1,100. Eleven hundred? Do you accept that? The tricky part is that if the image freezes at 500 rpm, the motor may go to 500 or 1,000, or 1,500 or 2,000 rpm. If we see a double image at a strobe frequency of 1,000 rpm, we can exclude 2,000 for the motor, but not 1,500. We try it on the whole spectrum so the student gets the full benefit," he says.

Lewin and Markos Hankin, a technical instructor in physics who is in charge of preparing the lecture demonstrations, tested with three assistants until 6:30 p.m. The next day, April 3, Lewin held a small ceremony in his classroom.

JungEun Lee, with a 4,700 rpm motor, was the winner. Lewin gave her a 25-inch-tall thermometer invented by Galileo Galilei that tells the temperature with small floating objects. "It's a charming and very romantic conversation piece," Lewin pointed out during the prize ceremony. "And it's not possible to get any lower-tech."

The rest of the top six are Adam Kumpf, whose motor ran at 4,100 rpm; Ryan Damico at 2,500; Philip Bramsen at 2,100; Emily Chang at 2,000 and Alexei Zykov at 2,000 rpm.

Tim Lo, who built a motor that ran at 1,250 rpm, won a prize for the most artistic motor. He received a book on modern art.

All six winners, plus unofficial contestant Daniel Wendel (who is not enrolled in 8.02 but managed to make a motor than ran at 4,900 rpm), have been invited to dinner with Lewin and Hankin on April 13 at ZuZu in Cambridge.

A version of this article appeared in MIT Tech Talk on April 10, 2002.

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