Portable consumer products such as music players, cameras and cell phones are becoming ever smaller. Miniaturized electronics deserve some of the credit, but so do ever shrinking motors. Most of them exploit the same physics principles as their bigger kin; the key is design and manufacturing ingenuity.

MP3 players such as the iPod provide an instructive example. They cram about 1,500 songs, or six gigabytes of data, per square inch of magnetic hard disk that is thinner than a dime. The disk is spun by a spindle motor. The rotor at its center is only two millimeters thick; it and other parts "would fit on the tip of your pinky," notes Hans Leuthold, head of motor R&D at Seagate Technology in Scotts Valley, Calif.