Sandwiched between two beds of nails topped with a cinder block and a sledgehammer-wielding colleague standing above him, College of DuPage Professor David Fazzini was ready to prove some physics Monday morning.

"Once again, I sacrifice my body for the benefit of your education," Fazzini told his class just before fellow physics professor Tom Carter smashed the cinder block into pieces.

The demonstration helps students see the difference between energy and momentum in action, albeit in a slightly bizarre manner. The cinder block absorbs the energy of the sledgehammer as it breaks apart and the momentum is transferred across the bed of nails. So instead of being impaled by hundreds of nails, Fazzini is left only with symmetrical indentations on the front and back of his torso.

"That's the making of a dedicated teacher," Carter said.

Though shirtless, Fazzini does wear a protective face shield, and students in the front of the classroom also wear protective glasses to ensure they aren't injured with flying shrapnel. No one's ever suffered an injury from the demonstration.

"It's never drawn blood," he said.

The duo have been doing the demonstration for about five years. It's done twice a year, and Fazzini is always on the receiving end.

"Can science get any more fun?" Carter asked. "I'd like to tell you my class is exciting as his, but it's not."

Fazzini claims that getting hit with a sledgehammer while resting between spike-laden boards is not the scariest part of the process. Instead, it's when he lies down and the second bed is placed on top of him.

"I have to lie down very gingerly," he said. "My greatest fear is that they'll drop the second board as they're moving it over me. That's why I have them bring it in low and away from my head."

The top bed has to be set in a sturdy enough spot so it won't slide when Carter destroys the cinder block.

"That may take a couple tries."

Only a few weeks into the semester, Fazzini said he's not done with the stunts.

"Wait until we get to the chapter on electricity," he said.

Physics: