A falling slinky may bring back fond childhood memories. Remember watching yours flip end over end as it wobbled its way downstairs? Or letting it dangle to see how far it would extend?
"Hold a slinky by its top and let it hang under gravity, and then release it," co-author Dr. Mike Wheatland, associate professor of physics at the University of Sydney in Australia, said in a written statement. "What happens next is not visible to your naked eye but, remarkably, the bottom section of the slinky remains suspended in midair until the entire top section collapses onto it."
Just watch closely in the video above--the slinky's bottom really does appear as if it's not moving. Weird.
"It takes a finite amount of time for the information or 'signal' about the changed conditions to be transmitted from the top to the bottom of the slinky," Wheatland explained. In the paper, Wheatland and his co-author report that a slinky's total "collapse time" corresponds to the time required for this "signal" to be transmitted from the top of the spring to the bottom.
"The falling slinky's behavior might seem counterintuitive, but physics can be like that," Wheatland said. "Dynamics--the interplay of forces around us--often need to be examined to become clear."