Richard James invented the Slinky along with his wife Betty. The couple was fearful that there would be no interest in such an ordinary looking toy. They were worried enough to give their own friend a dollar to buy one! After their first demonstration, they sold around 400 Slinkys. Slinkys were a hit.
The Slinky can perform a number of tricks. It stretches and reforms itself with the help of gravity. A Slinky will stay at rest without moving at all if placed on the floor or at the top of the stairs due to the resistance to change in its motion. But we notice that once it has started to fall down the stairs, gravity affects it. The potential energy is converted to the energy of motion or kinetic energy. Energy is transferred in a compression wave which is like a sound wave that travels through the Slinky. A pulse of energy moves from one molecule to the next. Factors such as the diameter of the coils and the height of a step is to be considered to understand why the Slinky moves the way it does.
A slinky looks as though it is levitating when dropped. In the article from Stanford’s “The Physics of a Falling Slinky” a thorough explanation is given as to why this is so. The bottom of the slinky is motionless while the top is collapsing on it. The equation for this, derived from Hooke’s Law (see picture)