A painful-looking video is starting to make its rounds on the Web.
It shows a man lying on the ground with a wooden board dotted with nails on his stomach. On top of the board is a cinder block. Above him stands an ax-wielding man. Then, in slow motion, the physics demonstration gone wrong plays out.
Instead of hitting the cinder block full on, the ax seems to only nick it and instead lands near the man's groin. Also in slow motion, the man on the ground curls up.
A GIF showing a different angle was posted by aderspatron on the social news site Reddit Tuesday.
"I don't have a longer video," aderspatron said in a comment. "This was my AP Physics teacher in high school, he does this demonstration every year. My friend who is still in high school sent me this video and the gif captures the whole thing. Also, that is another teacher who is swinging the axe lol."
Another Redditor going as haneefmubarak who claims to have witnessed the scene wrote, "The dude who was hit is the teacher. He was just fine - it was a graze - not a full on partitioning. The person holding the axe is a member of staff (either an assistant principal or a hall monitor) that we asked to come help with the demonstration."
"The teacher walked funny for like a couple of days and then he was just fine," haneefmubarak continued. "AP Physics I is fun because of stupid things like this happening."
Haneefmubarak said that the teacher involved got up after the demonstration was over and continued his lecture.
"Looked uncomfortable, but ya gotta do what ya gotta do," he wrote.
But without a longer version of the video — not to mention footage showing it happen in real time — or information about where exactly it happened, is all this legit? Some people speculated that this is another one of Jimmy Kimmels tricks, and it was posted just before April Fools Day after all.
The physics demonstration itself though, the Daily Dot pointed out, is a relatively common one. Harvard University's Faculty of Arts and Sciences explained on its website that the subject will often lie on a bed of nails as an added effect to demonstrate the force per unit. Here's how it all works, according to Harvard:
The forces (weight of the body, cinder block, etc.) are distributed over the total area of all the nail points so that the pressure is not high enough for the nails to puncture the skin. Of course we know what would happen if one were to lie on just one nail! In this case, the pressure is extremely high because the area of just one nail point is quite small.
A 2 cm (3/4") thick, 45 cm by 75 cm (1.5' × 2.5') plywood board has approximately 1,000 16-penny nails pounded into it so that they extend through the board. The nails are spaced about 2 cm apart. A similar board, but with twice the thickness (actually, just two boards together) of wood, is used for the top of the sandwich. One or two thick books (preferably physics books) serve as a pillow under the head.
Addition of the heavy top board plus the weight of the cinder block make it seem like one is adding to the difficulty of the demonstration. In fact, the additional weight makes it easier. The inertia of all this mass helps absorb the blow of the sledge hammer. Additionally, some of the sledge hammer's kinetic energy is dissipated by the fragmentation of the cinder block. For safety purposes, a plastic shield (with a U-shaped cut-out for the neck) as well as safety goggles are used to protect the subject's face and eyes from flying cinder block debris.
Here's an example of the demonstration being done with success:
We've reached out to aderspatron, haneefmubarak and Kunal Bhattacharjee, a person who claimed in the comments of another post that it happened at his school, for more details, but they did not immediately respond to our request for comment.