To understand how a turntable works, you first have to understand what parts are involved. A basic phonograph has three main components: the actual turntable (a circular base on which the record sits and spins), a tone arm and a stylus. The stylus is a small cone- or triangular-shaped tip that sits in and runs along the grooves of the record. The tone arm attaches to the stylus and holds it in place as the stylus moves over the record.
Every sound produces a measurable wave. These waves have force and produce significant vibrations--i.e., they are a form of energy that involves atomic movement. This means that people can convert vibrations into electricity, which is simply another form of energy. People do this with devices called transducers. It is this theory that serves as a foundation for phonograph function.
Turntableexperts.com states that when a phonograph is operating, the record spins around on the turntable. The stylus, held by the tone arm, travels along the grooves of the record from the outside inward. As the stylus travels along the grooves, it vibrates based on the tiny variations in the depth and width of the groove. The vibrations then travel to the end of the tone arm, where a cartridge receives them. A transducer (a coil in a magnetic field) in this cartridge converts the vibration to an electrical signal. These electrical signals travel through wires to the phonograph amplifier, where they are converted back to sound waves that can reach our ears.
Turntables are subject to multiple operational issues. First, if the turntable doesn't spin at an even speed, pitch levels may be inconsistent--some DJs use this effect intentionally according to Quezi.com, but for general listening where all a person wants to do is put on a record and relax, this is not desirable. Furthermore, Enjoythemusic.com explains that the weight of the stylus eventually wears on the groove of the record due to friction, resulting in loss of sound quality over time. Dust also may collect in the record grooves and on the stylus, resulting in unwanted hissing, pops or cracks.
Records are "lossless" recordings, meaning that no data is lost during the vibration-to-signal conversion process. This is different from many modern audio formats, in which some data automatically is "trashed" during conversion and compression processes. This is why some people prefer to operate phonographs instead of using modern recordings--lossless recordings provide better quality sound and a truer representation of the original recording.