The scroll wheel is made of hard plastic or rubber, since they are quite comfortable to touch and are a good materials since they are smooth so they can't harm anyone.en.wikipedia.orgScroll wheel - Wikipedia
The surface of the computer mouse is also made of ABS , because it is both hard and smooth. It is flat so that its easy to use and isn't uncomfortable. If the plastic wasn't smooth, then every time you clicked the mouse it would hurt you, and if it wasn't hared then each time you clicked it it would leave a dent which would be annoying.www.madehow.comHow computer mouse is made - manufacture, history, used, processing, parts, components, structure, steps, product
The chip, which converts the signal from the mouse to the computer is made up of silicon, because it is strong and flexible, as well as being a semi conductor
The bottom of the mouse is made of ABS plastic because it is strong and tough, but it is also durable which helps when you are using the mouse; if it wasn't durable, the material would wear off and the mouse would fall apart. Also it's smooth so when you are using it it won't scratch and damage the surface.
Screws are usually made of steel or other hard metals because that means that they are difficult to break, and it can also keep things in place. For example, id the screw would be made of a softer material, then it wouldn't be as good at keeping the two parts of the mouse together, and it would be harder to unscrew if you wanted to fix it.en.wikipedia.orgScrew - Wikipedia