You have to see it to believe it: Slinkies look crazy not just tumbling down stairs but in free fall. In a new video, YouTube's favorite Slow Mo Guys capture the puzzling dynamics of the iconic toy at 1,600 frames per second on a Phantom Flex camera. The video, which we discovered via the curators of awesomeness at Laughing Squid, is not the first to look at the phenomenon and the Slow Mo guys (Gavin Free and Daniel Gruchy) are willing to admit their take is not exactly super informative.
Luckily Rhett Allain, an associate professor of physics at Southeastern Louisiana University, has an in-depth look at the science at work over at Wired. He cites the YouTube series Vertiasium, which went viral with a similar falling-Slinky demo last fall. In the video below, physicist Rod Cross explains that the tension of the spring counters the pull of gravity ("equal and opposite forces"), holding the bottom end of the Slinky in place until it "gets the information that the tension has changed." By the time the bottom end of the Slinky gets the memo, the top end has fallen to meet it. What's true for Slinkies is also true in sports, including tennis rackets, according to Cross. Your hand doesn't feel the impact of a tennis racquet hitting a ball until the ball "is well on its way."
Allain takes the analysis further, modeling the Slinky in free fall by breaking it up into separate segments (top, center of mass, bottom) and graphing their positions over time. He even has a little gif demonstrating the motion. If the math is over your head, feel free to watch this Slinky strut its stuff a treadmill instead:
For more videos from the Slow Mo Guys, visit their YouTube channel.