In most computer
mice, these make contact with the mouse pad
and move the x and y roller
s inside the mouse, generating cursor movement. In well made mice
, they are heavy
(about thirty gram
s) and coated with slightly tacky rubber
. In cheaper mice, they are lighter weight and have a matte black coating. Optical
mice have an LED
instead of any gauche moving parts.
A local used computer store went out of business a few years ago, and sold off all of their merchandise for something like seventy percent off. Among the stuff offered for sale was a white box marked mouse balls on all six sides in red marker. I bought it immediately, and spent my entire walk home giggling. Nowadays the box sits in my room, and every once in a while a guest gives in to temptation and opens it. They are invariably less impressed with the contents than they thought they would be.