Physics professor uses a bed of nails to drive home a lesson

Vahe Peroomian winces slightly as he eases himself, with the help of two assistants, from a sitting position to lying full-length on a bed of long, sharp nails. Students in the room observe quietly as another plank of nails is placed onto his chest with their points down. As an assistant sets a cinderblock on top of it all, the students stir nervously, but Peroomian reassures them. “It’s just a bit more pressure,” he says.

Then the assistant reaches for a hammer, and the students erupt with excitement, cell phones recording.

The assistant moves into position near Peroomian and raises the hammer, taking aim. Then he strikes, shattering half of the cinder block, and the students let out a surprised exclamation: “Oooooo!” The tone suggests more than a little concern at their instructor’s well-being.

But they need not worry; Peroomian, professor (teaching) of physics and astronomy at the USC Dornsife College of Letters, Arts and Sciences, is fine.

His assistants clear the pieces of concrete, remove the top plank and help him stand, and he lets out a small “Whoo, all right!” The students applaud and cheer, clearly impressed — and likely a little relieved.

The demonstration is old hat for Peroomian; he’s performed the feat — and others — for more than two decades, including the 11 years he’s taught at USC Dornsife.

It’s part of his course “Fundamentals of Physics I: Mechanics and Thermodynamics” (PHYS 151) course, designed for students majoring in the physical sciences or engineering. The nail-bed demonstration aims to teach students about pressure and inertia.

By spreading his weight over many nails in the lower plank, no single nail will experience enough pressure to penetrate his back. And as the hammer strikes the cinder block, the block’s inertia absorbs the force of the hammer, keeping it from pushing the top plank of nails into his chest.

“I didn’t feel the concrete block,” he says. “I mean, it was heavy. It was sitting on top of me. But the additional impact of breaking it didn’t get through.”

The spectacle is intended to be entertaining and memorable, and for good reason: It drives the lesson home.

“I try to turn it into something tangible that the students can apply, and solidify their understanding of what’s going on,” Peroomian says. “Even if they only remember one demonstration that I did, that might help them if they’re struggling with the material.”