This is a story of a box truck and its bouncing baby box. An automatic transporation-focused Twitter bot named @tw_kotsujiko run by @90ntyan posted an amusing video this week of a storage box falling out of a moving truck and bouncing back into the truck's cargo area. What seemed to be a trick or prank of some sort was likely the result of a perfect blend of air flow and pressure that directed the box back to its home.
Via Jalopnik, the video was filmed on a highway in Asia. The box truck is seen driving with the rear door open and several pieces of cargo inside. Specifically, there appears to be at least three mid-sized boxes made of cardboard or styrofoam.
確かにトラックの後ろにはカルマン渦ができるけど— 台湾交通事故bot (@tw_kotsujiko) June 3, 2020
At six seconds in, the box falls, hits the pavement, does some flips, and drops right back into the truck. Then it falls off again, bounces again, and perfectly places itself in the corner of the truck, aligned with the other boxes. Despite the opportunity to venture into the great outdoors, the young box simply coudn't muster the will and might to leave the nest.
The text attached to the video roughly translates to, "certainly there is a Karman vortex behind the truck." A second translated comment reads, "Some people are debating Kármán vortex and slipstream, but they both mean the same phenomenon. The former is the 'vortex' that can be formed behind, the latter often refers to the act of using it." According to NASA, "von Kármán vortices arise when winds are diverted around a blunt, high-profile area," a phenomenon first described by physicist Theodore von Kármán in 1912.
We're not qualified to detail the exact science behind it, but basically the box, which apparently has nothing remotely weighted inside, falls out, is kicked up by one air stream, and is kicked back in by another. *Aaron Paul voice* Yeah, science!