Exploring the Science Behind the Bed of Nails

Upper School science students witnessed a hands-on demonstration of the relationship between force, pressure, area, inertia and acceleration as Science teachers Xiao Zhang and Natasha Itkin volunteered to lie down on a bed of nails.

Once a volunteer was in place, Science teacher George Austin—in costume as Fred Jones from Scooby Doo for Halloween—placed another wooden board topped with a cinder block on the volunteer's chest. Then he carefully raised a sledgehammer before bringing it down with all his might, crumbling the concrete and leaving the volunteer unharmed.

Following each demonstration, Austin explained to his Physics classes the variables and science at play. In this example, the force of gravity on each volunteer was supported by an equally large force from the nails, and the area was the area of the tip of the nails in contact with their body. Since this upward force from the nails was distributed over many nails on the bed, the pressure, or force per unit area, at the tip of any one nail was well below the level required to cause harm. Furthermore, because the cinder block has so much mass, its inertia provided sufficient resistance and did not accelerate into the board when the sledgehammer struck it. Instead, the block crumbled, keeping the volunteers protected from the effects of the blow.

A memorable Halloween lesson for all who shared it!

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