Yoyo
The yo-yo is a popular toy consisting of a length of string tied at one end to a flat spool.
It is played by holding the free end of the string (usually by inserting one finger in a slip knot) and pulling at it so as to cause the spool to turn whilst suspended in mid-air, either taking up or releasing the string.
First made popular in the 1920s, yo-yoing is still very much enjoyed by both children and adults, though it was originally made as a children's toy.
In the simplest play, the string is initially wound on the spool by hand; the yo-yo is then thrown downwards so that it first descends unwinding the string, then (by inertia) climbs back winding it up; and finally the yo-yo is grabbed, ready to be thrown again.
Many other trick plays exist, most based on the basic sleeper trick. One of the most famous tricks on the yoyo is "walk the dog".
This is done by throwing a strong sleeper and allowing the yoyo to roll across the floor.
English historical names for the yo-yo include bandalore (from French) and quiz.
French historical terms include bandalore, incroyable, de Coblenz, emigrette, and joujou de Normandie (joujou meaning little toy).
Physical Mechanism
The operation of a yo-yo comes from rotational inertia causing the string to be wound in the opposite direction returning the yo-yo.
When the string is connected to the shaft with a loop, the yo-yo will continue to spin at the end of the string instead of returning, unless the yo-yo is jerked slightly allowing the slack string to bind and allowing return.
Patents have been issued to create more complicated mechanisms to allow tension control and an adjustable mechanism.