“And of course you want it to be dramatic. Nothing all furled up and stationary, so the sails have to be out. Last time in the Keys, the shoot director didn’t hire enough people who knew what to do with sailboats. So when the booms were swinging around like baseball bats and models and photographers were ducking and covering left and right…”

“Oh no.” Jules laughed.

“Well, that’s just a question of torque,” Allie said casually.

Simon and Jules blinked at each other, then Simon turned to Allie. “Excuse me?”

“Oh, you know,” Allie said, smiling at him. “Torque. It’s just a vector that measures the tendency of a force to rotate an object around its axis. It’s one of the rotational analogs of force, mass, and acceleration. The closer you are to the axis, you know, the sail pole, the more force you need to move your object, like the boom, around it. But the farther out the object is, like the end of the boom, the less force you need to move it.”

“Um,” Jules said.

“Exactly! It’s like when you push open a door. You don’t press at it close to the hinge because that’s harder; you push it by the knob or the edge because that’s where it’s easier. You need less force. That’s sort of like when the wind moves the end of the boom around. It doesn’t take a lot of force, and next thing you know”—Allie swung her arm around in a wide arc—“whammo! So that’s torque. Force is the push, and torque is the twist.”

Simon and Jules stared at Allie with their jaws slowly sagging open.

“It’s simple,” Allie added. “I mean, that’s just the basics. You don’t really need to know all the formulae. Although it gets interesting once you start working out the scalar product of two vectors.”

“Oh,” Jules said.

“Anyway, just make sure the booms are stable where they connect to the poles,” Allie added, beaming at them, “so the wind would have to exert a lot more force if it wants to move the ends. Maybe some kind of buttress, just for the photoshoot. I can draw you a diagram”—she blushed—“if you think it would help.”

“I…” Simon said. “Uh…”

“Allie,” Jules said, and blinked rapidly. “How do you know all that?”

“Oh!” Allie’s face brightened. “I’m double-majoring in physics and media at NYU. I didn’t put the physics major on my résumé, though. I didn’t think it would look very stylish.”

“Um—”

“My advisor said I should think about grad school and a career in astrophysics, but I told him that fashion was my passion.” She suddenly smiled again. “Hey, that rhymed.”

“Rhymed,” Simon said. “Yes.”