Last night, I went out and saw the movie Split. I was slightly intrigued by the reviews, and it was said to have a really surprising ending, so I put aside some of my personal opinions on the topic of choice and watched it.
It was a very interesting movie to say the least, and if you're planning on watching the movie, I would stop reading here, because in order to get into some physics I have to spoil the ending, which is entirely the best part.
Okay, now that you're sure you want to continue, the movie is about a man with 23 distinct personalities inside him, which all take control at different times. While one, Barry, is in control, he kidnaps three girls. Three of the personalities (Barry, Ms. Patricia, Hedwig) believe in a figure called the Beast. The spectators find out that the Beast is not a figment of their imaginations, but actually a 24th personality that has super powers. Just by switching to this personality, the man's body becomes impenetrable and extremely strong.
The only surviving girl, Casey, tries to shoot him with a shotgun and the bullet essentially bounces right off. That's where the physics comes in. How much force would a regular shotgun shell impart, and how strong would this man's skin have to be?
A 1 oz. shotgun slug leaves the shotgun at 1800 fps, or about 550 m/s. This slug would weigh about .03 kg, giving it a momentum of 16.5 kg m/s. Assuming that the bullet was only in contact with his skin for .001 seconds, and it was a perfectly elastic collision, the force imparted onto his skin would be 16500 N. The only metal I could find info on was steel, and it can withstand 40 kN, meaning that his skin could withstand atleast half the force steel can.