I had a slinky as a child and loved it. Initially because if you stretched it out a little bit and peered inside, it looked similar to this (alas no Tom Baker would appear at the other end). And then because it walked down stairs. All by itself. How did it do that? In that respect, a slinky is a fantastic tool for understanding physics. What is going on in a slinky that makes it able to walk down stairs or in the above instance a treadmill? Or perhaps a simpler question: what happens if you hold a slinky up so that its coils stretch down to just above the ground and then drop it? Continue reading