Few toys created have been as popular as the famous Slinky, which first hit shelves in 1946. The first 400 units sold in 90 minutes which, considering the absence of internet and global reach we enjoy today, is a lot! Now that you’re reminiscing about gleefully nudging a Slinky down the stairs as a child, let us drop another fun fact on you. Slinkies can levitate…

… sort of. They can’t really levitate, but for a short period of time it certainly looks that way. In a video made by YouTuber Veritasium, the host shows that dropping a Slinky from one end while fully extended creates a head-scratching levitating effect at the other end.

We were intrigued enough to recreate this process using Altair solutions to figure out what causes this illusion.

Setting Up

To recreate this test, we used Altair® Radioss®, our leading analysis solution that evaluates and optimizes product performance for nonlinear problems under dynamic loadings. Used worldwide across all industry sectors, Radioss improves complex designs’ crashworthiness, safety, and manufacturability.

After creating the model in Radioss, we positioned the Slinky to be fully extended under the force of gravity and in a state of equilibrium. This meant that all acting forces were cancelled out, which gives us a stable, balanced Slinky. As you can see from the video below, the accurate results are just as curious.

A Logical Explanation

So, what’s happening here?

Simply put, the bottom of the Slinky is pulled down by gravity and up by tension – as such, this counteraction creates equal and opposite forces. As the top falls, a compressional wave transmits information about the change in tensional force but takes time to reach the other end. This results in a short-lived, seemingly gravity-defying levitation act.

Conclusion

It’s safe to say the levitating ability of a Slinky, or lack thereof, was always obvious. We suspect that if Slinkies could really levitate, they’d be a much more popular piece of technology; imagine an alternate universe where humans developed anti-gravity aircraft powered by Slinky technology – one can only dream of such a spectacle! Anti-gravity or not, recreating this cool trick was always on our bucket list. If you’re lucky enough to still have a Slinky, dig it out and try it yourself. Don’t blink though – you might miss it.

Veritasium is a YouTube channel dedicated to showing the beautiful side of science. Be sure to check the channel out for more cool videos!