4. The Slinky
Now, the slinky probably isn’t something that you use on an everyday basis, but at some point in your childhood I’m sure you played with one. I remember letting mine slowly fall from the top of the staircase all the way to the very last step at the bottom, watching it as if it had a life of its own. Navy engineer Richard James accidentally created the slinky when he was trying to design a way to protect vital instruments from moving and getting damaged during motion. After dropping a tension spring and noticing the bounce it had when it returned upright, the slinky was naturally and accidentally created in an instant.