High-speed video reveals the bizarre physics of Slinkys

And now, for your Monday morning moment of zen, Slinkys in slow motion. Whether it's dropped from eye level, or from the roof of a building, the bottom of a fully extended slinky will appear to hover in midair when released.


What lets the Slinky's bottom hover like that? It all boils down to the summation of forces. Remember: a Slinky is just a big, loose spring. When the spring is fully extended like you see in the video, it has reached a point of equilibrium wherein the the downward force of gravity is equal and opposite to the upward tension of the coils above the bottommost end of the Slinky.

When released, the top of the Slinky has two forces acting on it: the force of gravity, and the force of the spring, which is also pulling it downward. The bottom of the slinky has two forces acting on it, as well; the difference is that while gravity is still pulling downward, the force of the spring's tension is instead pulling the bottommost coils upward. The two forces cancel eachother out, hence the hovering effect.

By the same logic, the fully stretched Slinky's center of mass experiences equal spring tension from both sides of the slinky. These forces cancel one another out, so the CoM falls toward the ground at the standard 9.8 m/s2. To quote Bill Unruh, a physics professor at the University of British Columbia who recently wrote this awesome paper describing Slinky physics (including its behavior on other planets): "There is a lot of interesting physics in a very, very simple system." [Veritasium and arXiv via Explore]


Aha! According to my calculations, this study will finally allow for flying cars. Simply replace the tires with the bottom halves of slinkies, while cutting off the top half.