1. Field of the Invention
The present invention generally relates to yo-yos, and pertains particularly to a yo-yo having an optimized rotational inertia with a string finger guard.
2. Discussion of the Related Art
Yo-Yos are popular toys which consist of two disk-like structures that are positioned axially adjacent to each other on an axle and having a string that is connected to the finger of a player when in use. The player "throws" the yo-yo, transferring kinetic energy to the yo-yo, which unwinds the string causing the yo-yo to spin about its axle. Tricks must be performed quickly while the yo-yo is spinning so that the yo-yo has enough kinetic energy at the end of the trick to return up the string into the hand of the player. Thus, a yo-yo that has a long spin time allows the player to perform difficult tricks and increases enjoyment of the toy.
The kinetic energy, K, of a spinning, or rotating rigid body like a yo-yo is expressed by the equation: K=1/2I.omega..sup.2, where ".omega." is the angular speed about an axis (the axle), and "I" is the rotational inertia of the rigid body. I is a measure of the resistance a body offers to a change in its rotational motion about a given axis. So a yo-yo with a large I, or rotational inertia will resist any change in its rotational motion and spin for a longer period of time. Rotational inertia is unique to each physical shape. For a solid disk having uniform thickness and density, similar to many yo-yos, I=1/2MR.sup.2, where R is the radius of a uniform disk of mass M. Where the mass M is positioned at a specific radius, as in a hoop, or ring, I=MR.sup.2, which is twice the rotational inertia of a disk where the mass is distributed uniformly along the disk radius. Therefore, the rotational inertia, and thus the propensity for a yo-yo to remain spinning can be increased by locating the mass of the yo-yo as far away from the axle, or rotational axis as possible. In other words, maximizing the rotational inertia of a given yo-yo mass maximizes the efficiency and performance of the yo-yo, resulting in a superior toy.
Also, a yo-yo must fit comfortably in the hand of a player and therefore a yo-yo cannot be too large in diameter. Until now yo-yo design was driven by cost considerations, and cost-effective plastic injection-molded yo-yos have dominated the child and young adult market, but are limited in their spinning performance due to the limited material that can be distributed about the yo-yos periphery. However, yo-yos and the relaxation of yo-yo playing are appealing to adults who have the resources to purchase more expensive, and sophisticated Yo-yos with optimized spinning performance. Accordingly, there is a need for an improved yo-yo having high efficiency and performance characteristics.
However, a yo-yo with enhanced performance exerts higher stresses on the yo-yo string which is attached to the finger of the player. This woven cotton string is also known as a standard twisted pair strand tether. As shown in FIG. 6, the yo-yo string has a relatively small diameter and is usually attached to the middle finger of the throwing hand. The prior method of attachment to the finger is to tie a loop at the end of string and then pull a section of string through the loop forming a noose that is pulled over the finger (FIG. 6). As the player repeatedly throws the yo-yo the noose squeezes and pinches the finger. The pinching of the noose around the player's finger causes discomfort and restricts blood flow to the finger, thus limiting playing time and distracting from the enjoyment of playing with the toy. Accordingly, there is a need for a device that connects the yo-yo to the player's finger and that does not cause discomfort and permits unlimited playing time.