A volunteer lies on a bed of nails at Six Flags Physics Day on April 26, 2013.
Image Credit: Matt Payne/AAPT
Every year, several physics organizations including the American Physical Society team up to host Six Flags Physics Day in Bowie, MD. The project aims to connect theme park fun with the physics principles behind the thrills.
Physics demonstrations are sprinkled throughout the park, including the bed of nails pictured above. So why didn't the bed of nails pierce the brave volunteer's skin?
It all comes down to pressure, or the force per unit area. When lying on a bed of nails, our body exerts a force equal to our weight. Although that's a significant amount of force, all of that force is distributed across the hundreds of closely-spaced nails on the bed.
When there's plenty of nails, the pressure any single nail exerts on the skin is quite small, resulting in no pain and no cuts. Resting an entire body on a single nail, however, would be a different story.