Microphone
Dynamic - This uses a round plastic or rubber disk connected to a wire coil in order to turn sound into electricity.  The sound wave hits the disk which vibrates as a result.  This vibration moves the coil back and forth near a magnet very quickly in order to create an electrical current.  The dynamic microphone is the exact opposite of a speaker which uses an electrical current to move the coil, which moves the disk.  Then the disk makes sound.