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A spinning top is a toy designed to spin rapidly on the ground, the motion of which causes it to remain precisely balanced on its tip because of its rotational inertia. Such toys have existed since antiquity. Traditionally tops were constructed of wood, sometimes with an iron tip, and would be set in motion by aid of a string or rope coiled around its axis which, when pulled quickly, caused a rapid unwinding that would set the top in motion. Today they are often built of plastic, and modern materials and manufacturing processes allow tops to be constructed with such precise balance that they can be set in motion by a simple twist of the fingers and twirl of the wrist without need for string or rope.
Contents
Characteristics
The motion of a top is produced in the most simple forms by twirling the stem using the fingers. More sophisticated tops are spun by holding the axis firmly while pulling a string or twisting a stick or pushing an auger. In the kinds with an auger, an internal weight rotates, producing an overall circular motion. Some tops can be thrown, while firmly grasping a string that had been tightly wound around the stem, and the centrifugal force generated by the unwinding motion of the string will set them spinning upon touching ground.
The top is one of the oldest recognizable toys found on archaeological sites. Spinning tops originated independently in cultures all over the world. Besides toys, tops have also historically been used for gambling and prophecy. Some role-playing games use tops to augment dice in generating randomized results; it is in this case referred to as a spinner. A thumbtack may also be made to spin on the same principles.
The action of a top is described by equations of rigid body dynamics (see the section Rotation in three dimensions). Typically the top will at first wobble until the shape of the tip and its interaction with the surface force it upright; contrary to what is sometimes assumed, longstanding scientific studies (and easy experimentations reproducible by anyone) show that less friction increases the time before the upright position is reached (unless the top is so unbalanced that it falls before reaching it). After spinning upright (in the so-called "sleep" position) for an extended period, the angular momentum will gradually lessen (mainly due to friction), leading to ever increasing precession, finally causing the top to topple in a frequently violent last thrash. In the "sleep" period, and only in it, provided it is ever reached, less friction means longer "sleep" time (whence the common error that less friction implies longer global spinning time)
There have been many developments within the technology of the top. Bearing tops, with a tip made of a small hard ceramic, tungsten carbide or even ruby ball (sometimes wrongly believed to spin with respect to the body of the top), have been one of the biggest changes. In addition, plastic and metal have largely supplanted the use of wood in tops. Fixed tip tops are featured in National Championships in Chico, California and in the World Championships in Orlando, Florida.
The following two well-known characteristics of a top that increase its global spinning time () are exploited in various ways in such championships and by the main top makers (obviously, an optimisation of both characteristics has to be somehow restricted by conditions on mass and/or diameter and by practical considerations about the rim not touching the spinning surface too early):
- low center of gravity
- high moment of inertia
A top may also be used to demonstrate visual properties, such as by James David Forbes and James Clerk Maxwell in Maxwell's disc (see color triangle). By rapidly spinning the top, Forbes created the illusion of a single color that was a mixture of the primaries:
[The] experiments of Professor J. D. Forbes, which I witnessed in 1849… [established] that blue and yellow do not make green, but a pinkish tint, when neither prevails in the combination…[and the] result of mixing yellow and blue was, I believe, not previously known.
Maxwell took this a step further by using a circular scale around the rim with which to measure the ratios of the primaries, choosing vermilion (V), emerald (EG), and ultramarine (U).
Asymmetric tops of virtually any shape can also be created and designed to balance.
Notable types
In popular culture
The Jean Shepherd story, "Scut Farkas and the Murderous Mariah" revolves around top-spinning in the fictional Depression-era American city of Hohman, Indiana. The bully and the named top in the title are challenged by Shepherd's ongoing protagonist Ralph and a so-called "gypsy top" of similar design to Mariah named Wolf.