A yo-yo (also spelled yoyo) is a toy consisting of an axle connected to two disks, and a string looped around the axle, similar to a spool.
It is played by holding the free end of the string known as the handle (by inserting one finger—usually the middle or index finger—into a slip knot), allowing gravity (or the force of a throw and gravity) to spin the yo-yo and unwind the string (similar to how a pullstring works). The player then allows the yo-yo to wind itself back to the player's hand, exploiting its spin (and the associated rotational energy). This is often called "yo-yoing".
The sleeper is one of the most common yo-yo throws and is the basis for nearly all yo-yo throws other than looping.
Keeping a yo-yo spinning while remaining at the end of its uncoiled string is known as sleeping. While the yo-yo is in the "sleeping" state at the end of the string, one can then execute tricks like "walk the dog", "around the world", or the more complex "rock the baby".
In competition, mastery of sleeping is the basis for the 1A division.
Inexpensive fixed-axle yo-yos usually spin between 10–20 seconds, while the expensive ball bearing yo-yos can spin about 1-4 minutes depending on the throw.
As of 2010, the world record sleep times were 3:51.54 minutes for fixed-axle and 21:15.17 minutes for transaxle yo-yos.
In 2012, the transaxle yo-yo sleep time record was broken by the C3YoyoDesign BTH, with a time of 30:28.30 minutes.
Most modern yo-yos have a transaxle or ball bearing to assist this, but if it is a fixed axle yo-yo, the tension must be loose enough to allow this.
The two main ways to do this are, allow the yo-yo to sit at the bottom of the string to unwind, or perform lariat or UFO to loosen the tension. When one decides to end the "sleeping" state, one merely jerks the wrist and the yo-yo "catches" the string and rolls back up to the hand. Ball-bearing yo-yos with a "butterfly" shape, primarily used for string tricks, frequently have low response or are completely unresponsive, requiring a "bind" for the yo-yo to return".