The Slinky is a helical spring toy invented and developed by American naval engineer Richard T. James in 1943 and successfully demonstrated at Gimbels department store in Philadelphia on November 27, 1945. It can perform a number of tricks, including travelling down a flight of steps end-over-end as it stretches and re-forms itself with the aid of gravity and its own momentum; and appearing to levitate for a period of time after it has been dropped. These interesting characteristics have contributed to its success in its home country of the United States, and it has inspired many popular toys with Slinky-like components, in a wide range of countries.
History
Creation In 1943, Richard T. James, a naval mechanical engineer, observed a spring "stepping" downward after being knocked off a shelf, then coming to rest in a vertical position. James's wife Betty later recalled, "He came home and said, 'I think if I got the right property of steel and the right tension, I could make it walk.'" James experimented with different types of steel wire over the next year, and finally found a spring that would "walk". Betty was skeptical, but changed her mind when the toy was fine-tuned and neighborhood children expressed an excited interest in it.
Richard and Betty formed James Industries and began manufacturing Slinkys in Clifton Heights, Pennsylvania, selling them for $1 each. They were 2+1⁄2 inches (64 mm) tall, and included 98 coils of high-grade blue-black Swedish steel. They initially had difficulty selling Slinky to toy stores, but in 1945, they were granted permission to set up an inclined plane in the toy section of Gimbels Department Store in Philadelphia to demonstrate it on the Tuesday after Thanksgiving. It was an instant hit; the first 400 units were sold in 90 minutes. In 1946, Slinky was introduced at the American Toy Fair. Although the Slinky was originally priced at $1, many later paid much more, due to price increases for spring steel in Pennsylvania. It has, however, remained modestly priced throughout its history as a result of Betty James' concern about the toy's affordability for less affluent customers. In addition to its use as a toy, it has been used as a classroom teaching tool, and also as a portable and extendable radio antenna in the battlefield (particularly in the Vietnam War). It was inducted into the National Toy Hall of Fame at The Strong in Rochester, New York in 2000. In 2003, it was included in the Toy Industry Association's Century of Toys List. In its first 60 years, about 300 million Slinkys were sold.
Subsequent developments Although the Slinky had early success, sales peaked in the late 1950s, then began to decline. Richard's interest in Slinky and the company waned, and he became deeply involved in a religious sect, reportedly giving it large amounts of company funds. In 1960, he told Betty that he was going to become an evangelical missionary in Bolivia with Wycliffe Bible Translators. Rather than going with him or selling the company, Betty decided to remain, divorce Richard, and take over the company. Richard relocated to Bolivia leaving Betty and their six children behind. Betty James moved the company to Hollidaysburg, Pennsylvania in 1964 and the company grew under her direction. She attributed the toy's success to its "simplicity". The company was sold to Poof Products, Inc. in 1998. Slinky continued production in Hollidaysburg. Betty James died of congestive heart failure in November 2008, at age 90, after serving as James Industries' president from 1960 to 1998. In July 2012, Poof-Slinky, Inc. was acquired by the private equity firm Propel Equity Partners. In 2014, Propel Equity Partners consolidated Poof-Slinky and several other toy brands into Alex Brands. In July 2020, the Slinky brand was sold to Just Play.
Physical properties The physical laws that govern the mechanics of a Slinky are Hooke's law and gravitation.
Period of oscillation The oscillation of a vertically suspended Slinky has the periodic duration
T = 32 L g , {\displaystyle T={\sqrt {\frac {32L}{g}}}\,,}
where L {\textstyle L} is the length of the Slinky, and g {\textstyle g} the acceleration due to gravity, approximately g = 9.81 m / s 2 {\textstyle g=9.81\,\mathrm {m/s} ^{2}} . The expression for T {\textstyle T} is independent of the spring constant k {\textstyle k} and the mass m {\textstyle m} of the Slinky. For a spring pendulum one would expect such a dependence. This is because the dependence on k {\textstyle k} and m {\textstyle m} is hidden in the length L ( k , m ) {\textstyle L(k,m)} :
L ( k , m ) = m g 2 k = W 2 k {\displaystyle L(k,m)={\frac {mg}{2k}}={\frac {W}{2k}}} (W is the weight). This allows one to write:
T = 4 m k . {\displaystyle T=4{\sqrt {\frac {m}{k}}}\,.}
This expression differs from the ordinary spring pendulum
T spring pendulum = 2 π m k {\displaystyle T_{\mbox{spring pendulum}}=2\pi {\sqrt {\frac {m}{k}}}}
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