You probably have the childhood memories of watching the Slinky walk its way down the stairs. The helical (螺旋形的) spring toy was invented by Richard James in 1943. While James was testing ways to keep equipment safe on the U. S. Navy Ships, one of the springs fell and began to "walk". Seeing the spring can be marketed as a toy, he took the idea home to his wife Betty, who named it the Slinky after looking through a dictionary.
In 1945, James perfected the design of the Slinky, which was about 24 metres of wire shaped into a helical five centimetre-tall spring. The new product was a hit: By the end of the 1945 holiday season 22, 000 Slinkys had been sold. It went on to become the must-have toy of the mid to late 20th century. Many reasons have been given for the Slinky's popularity: "It's cheap." "It teaches kids physics." "Children love simple things." and so on.
As a child, making a Slinky step perfectly from the top of the stairs to the bottom is exciting. The Slinky gets its "walking" ability from two properties: wave motions and Newton's laws. Sitting at the top of the stairs, the Slinky remains-unchanged, like all objects that are not being moved by other forces. When the Slinky is knocked off the first step, gravity acts upon its coil. Then energy is transferred (传递) from coil to coil until it arrives at the end of the slinky, which makes it stretch to reach the next step down, reform itself, then stretch again to reach the next step, and so on.
