What makes modern physics so darn important and quintessential to society is its ability to predict future events. Armed with knowledge of how nature responds to our cues, we know how to design safe airplanes, build cars or land on the moon. To prove a point, Norwegian Physicist Andreas Wahl submerged himself in a pool and fired a rifle pointed at himself. Counting down from three, Wahl pulls a long rope rigged to the weapon’s trigger. Was he mad? More like confident in how physics works.
Predictably, the bullet didn’t even travel half-way to this torso. Outside, through air, the bullet would have fatally punctured him.
Why the bullet stopped had nothing to do with the gun being underwater. Guns works just as well in air or water. The bullet exits the chamber underwater with the same force it would have above the surface. It’s just that once propelled from the barrel, the drag between the bullet and the water molecules quickly deaccelerates the projectile from roughly 700 miles/hour to a full stop just a couple of feet from rifle itself. Since water molecules are closer together than those in air, the difference in density is about 800 fold.
With this in mind, is Wahl a daredevil or a showoff?