The AK-47 is an iconic assault rifle, popular among revolutionaries and known for its rugged, reliable design. Thanks to the team at Smarter Every Day and The Slow Mo Guys, the AK-47 is also a way to learn about physics! Underwater, the bullet travels only about 5 to 6 feet (in the air, it can travel some 1,300 feet). That's neat if unsurprising; water is much denser than air and puts up greater resistance. The real science clocks in at the 6-minute mark, in an explanation of how bubbles work underwater and the way pressure from the bullet turns water to vapor before the round has even left the barrel. Cool! Now I'll make sure I always have at least a 6-foot layer of water around me in a gunfight.