Computer mice, or some people say mouses, are everywhere now. Your question is a good one. Our computing scientist, Pierre Kerr, ac210@freenet.carleton.ca, gave us this answer.

When I saw your question I immediately got an old computer mouse and took it apart. I knew there was a ball in a mouse but I wanted to see what exactly it did. If you look on in the science corner in the school library, you'll see the mouse that I cut open. You can move it around and see what happens to the ball.

A mouse is used to control a cursor (usually an arrow or flashing dash), on the computer screen. There are and have been many other ways to move a cursor including a cat, track ball, joystick, light pen, thumb wheels, touch screen and cursor or arrow keys. Out of all of those, the arrow keys are still used and the touch screen is becoming popular again. Joysticks and trackballs are used more in game playing.

You probably want to know what the cat was. Well, Xerox made a computer that was used only for word processing. It had a circular area at the right hand side of the keyboard where you would place your pointer finger. By rubbing it from one side to the other you would move the screen cursor. It was sort of like tickling a cat's tummy.

Anyway, back to your question. The ball, as you can see if you look at the one in the library, rolls in the direction that you push the mouse. This motion is transferred to two small wheels inside the mouse that rub against the mouse. These wheels turn things that look a bit like gears with teeth. These spin between a small light and a detector than knows when the light is blocked by a tooth or not.

The mouse sends electrical signals along the wire connecting it to the computer that change according to the light detected. The computer can then figure out which direction and how fast the mouse was moved.

The mouse pad is designed so that the mouse can move smoothly back and forth while the ball can grip enough so that it accurately tracks the motion of the mouse. A bumpy surface will cause the ball to skip and a sticky surface will make your hand and arm tired. Most mouse pads are smooth and fairly hard.

Answer #% % filename A119.DOC page% % page 1 of% % numpages 1 % % date \@ "MMMM d, yyyy"June 17, 1995