The Science Behind Slinkys®… Part One: The Vertical Drop
by Jill Mayer
I grew up playing with Slinkys® -- walking mine down the stairs, passing it from hand to hand, creating funny sounds, making waves, using it as a cage for smaller toys, tangling it up and then trying to untangle it. For some strange reason it never worked the same after becoming a snarled mess, even if I could untangle it. ☹ Then I had to convince my parents to get a new one for me!
One trick I never tried was to hold on to one end, letting the other end dangle, and then dropping the Slinky to the ground. So recently when I was chatting with my friends, we got into a friendly debate about what would really happen when dropping a Slinky.
Does the whole thing fall at once, does the bottom rise to meet the top before it falls, do both ends contract to the middle before it falls, or does the bottom hover in midair while the top falls to meet the bottom and then the whole thing drops to the ground?
When we actually tried it, it moved so fast we couldn’t tell what happened! The following video sets up the experiment. After you watch it, think about what you think will happen.
Dr. Derek Muller, our guest from Veritasium, interviews Associate Professor Rod Cross, a physicist from the University of Sydney, Australia. In this video, they talk about dropping the slinky, and list 4 possible outcomes.
Before you watch the next video, which shows the dropping Slinky, make YOUR prediction!
Were you surprised? Did you make the right prediction? Now what do think will happen if we attach a tennis ball to the bottom of the Slinky and then drop it? Will the same thing happen, or will the weight of the tennis ball make it do something different?
Now go try it for yourself! Send us a note telling us about YOUR Slinky drop experiment. What questions do you have?