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Liquid-Filled Top


These liquid-filled glass dreidels exhibit interesting physics.

When spun, the colored water in the internal cavity exhibits interesting physics to keep the top spinning.

Includes stand.
Dimensions: 3" tall x 1 ½" diameter

further research
further research

A spinning top, or simply a top, is a toy with a squat body and a sharp point at the bottom, designed to be spun on its vertical axis, balancing on the tip due to the gyroscopic effect. Once set in motion, a top will usually wobble for a few seconds, spin upright for a while, then start to wobble again with increasing amplitude as it loses energy (angular momentum), and finally tip over and roll on its side. Tops exist in many variations and materials, chiefly wood, metal, and plastic, often with a metal tip. They may be set in motion by twirling a handle with the fingers, by pulling a rope coiled around the body, or by means of a built-in auger (spiral plunger). Such toys have been used since antiquity in solitary or competitive children games, where each player tries to keep one's top spinning for as long as possible, or achieve some other goal. Some tops have faceted bodies with symbols or inscriptions, and are used like dice to inject randomness into games, or for divination and ritual purposes. The ubiquity of spinning tops lends to the fact that the toy is used to name many living things such as Cyclosa turbinata, whose name comes from the Latin roots for spinning top.

The motion of a top is described by equations of rigid body dynamics, specifically the theory of rotating rigid bodies). Because of the small contact area between the tip and the underlying surface, and the large rotational inertia of its body, a top that is started on a hard surface will usually keep spinning for tens of seconds or more, even without additional energy input. Typically the top will at first wobble until friction and torque between the tip and the underlying surface force it to spin with the axis steady and upright. Contrary to what is sometimes assumed, longstanding scientific studies (and easy experimentations reproducible by anyone) show that reducing the friction increases the time needed to reach this stable state (unless the top is so unbalanced that it falls over 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 and roll some distance on its side. 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). The total spinning time of a top is generally increased by increasing its moment of inertia and lowering its center of gravity. These variables however are constrained by the need to prevent the body from touching the ground. Asymmetric tops of virtually any shape can also be created and designed to balance.