Write short notes on the following: Track ball

Trackball: A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes - like an upside-down mouse with an exposed protruding ball. It is mechanical in nature and available in two and three button models. The user rolls the ball with the thumb, fingers, or the palm of the hand to move a pointer. Compared with a mouse, a trackball has no limits on effective travel, at times, a mouse can reach an edge of its working area while the operator still wishes to move the screen pointer farther. With a trackball, the operator just continues rolling. Some trackballs, such as Logitech's optical-pickoff types, have notably low friction, as well as being dense (glass), so they can be spun to make them coast.