How does a vibrating cell phone or pager work?
If you have a cell phone or a pager, then you know that having it ring in the middle of a movie or performance is enough to get you killed in some cities. Vibrating devices that quietly replace the ringer are therefore life-saving devices that are an important part of urban survival! There is, however, a device that takes vibration to high-tech extremes. Any parent whose child owns a Tickle-Me-Elmo doll has experienced this technology. Elmo has a vibration system (designed to simulate body-shaking laughter) that is powerful enough to cause many children to drop the toy. The vibration system inside a pager works exactly the same way on a smaller scale, so let’s use Elmo as an example. Here is a Tickle-Me-Elmo doll: Minor surgery reveals the control unit: Inside the control unit (on the right hand side in the above image) is a small DC motor which drives this gear: You can see that, attached to the gear, there is a small weight. This weight is about the size of a
