So, how about a little on topic?
A cartridge is a small electrical generator, which is a device for transforming mechanical energy into electrical energy. It was observed during experimentation in the 1800's that when a wire moves through a magnetic field, an electrical current is generated in the wire. When the movement stops, the current stops. Generators work by placing wires and magnets next to each other and moving one or the other in some type of rotary or back and forth motion. A generator in a hydroelectric power plant produces electrical power when its turbine is turned by the flow of water. A phonograph cartridge produces a tiny bit of power (which is another way of saying there is current and voltage) when its stylus vibrates (moves back and forth) through the record groove.
If you and I are in a room speaking to each other, your vocal cords vibrate as the air you exhale through your windpipe passes by them. The vibrating vocal cords disturb the air in a particular pattern, which I perceive as speech. The molecules of air exiting your mouth bump into the molecules of air that are in the room, setting them into motion. Those molecules then start travelling, and bump into others next to them, and so on. In this way, sound travels (or is propagated) through air. Eventually, the air sitting next to my eardrum is disturbed, pushing on my eardrum, and I perceive the sound of your voice.
The first phonographs copied the eardrum, but it's called a diaphragm. Just another word for the same thing. A diaphragm is a thin sheet stretched on a frame, like a canvas on a painting, but diaphragms are usually round and dome shaped. When an object is said to be stiff or rigid, it means that the object resists being deformed, and when it is deformed, it tends to go back to its original shape and position. Pliable is the opposite of stiff. If a thin membrane of a pliable material is mounted on a frame and placed under tension, its stiffness is increased. So, of a membrane under tension is moved from its rest position by, say, a sound wave hitting it, it tends to return to its rest position. Hit it with another sound impulse, and it is deflected again, then returns to rest position. Keep repeating this in rapid succession, and a continuous vibration is set up. Thomas Edison found that if he connected a diaphragm to a needle, when the diaphragm was put in motion by a sound wave, the diaphragm would push on the needle and the needle would vibrate. He coated a cardboard tube with a layer of wax. He put the wax coated tube on a mechanical roller and started it turning. He then placed the needle (connected to the diaphragm) in contact with the wax on the tube, allowing the needle to cut a groove into the wax. Without sound, the diaphragm didn't vibrate, and the groove was a straight, V shaped trough with smooth, straight sides. But if sound was present, the diaphragm would vibrate, which would push on and wiggle the needle as the wax tube spun, making a groove with a curvy path. The wax cylinder was then sold to a buyer who had a reproducer at home. The reproducer had a device to mount the cylinder on and spin it, and it had a needle connected to a diaphragm. When the reproducer needle was placed on the wax cylinder, the groove in the wax caught the needle. The needle followed the curvy groove was moved back and forth in a vibratory motion, and pushed on the diaphragm connected to the needle. The diaphragm pushed on the air in the listener's room, and created a sound wave.
That's how it was for decades. Purely mechanical/acoustic. A guy named Berliner invented the disc format (among other impressive innovations), but it worked on the same basic principles. Instead of a wax coated paper cylinder, he used a disc made of rubber. Eventually, a composite of shellac with other materials become the most common way to make discs. In the mid 1920's, people started using microphones connected to tube amps to capture the sound, which required modifications to the method. This method converts the mechanical energy of a sound wave into electrical energy. Microphones and phono cartridges can both be called pickups because they both convert mechanical energy into electricity, even though they differ mechanically. The amp was then connected to a motor. A motor works on the same principles as a generator, but in reverse. So, a motor converts electrical energy into mechanical energy. The microphone is connected to an amp, the amp to a motor, and the motor to a cutting needle (or cutter, for short). Also, they would take a metal platter and coat the platter with acetate. Acetate is soft but moldable, much like wax. Later, lacquer was used instead of acetate, and lacquer is still used to this day. Anyway, the cutter was placed into the acetate on the spinning platter. During recording (sound capture), the microphone detected the sound, converted it to electricity, the electricity power was boosted by the amp to a level sufficient to drive the cutter motor, the motor wiggled the cutter, the cutter sliced a curvy groove into the acetate. While all of that was a significant change from the past, the play back machines didn't change right away. They didn't have to. The technology was backwards compatible, and electrically recorded discs could be played on an acoustic machine. Before 1930 though, electrical reproducers became available for home use. Which required the use of cartridges working on principles similar to what we use today.
In a contemporary (present day) turntable, the stylus vibrates as it rides in the groove of a record spun by the platter. As it rides, the stylus vibrates back and forth. The stylus is connected to a either a magnet that moves past a coil, or a coil that moves past a magnet. There is a third type, called moving iron, where the stylus is connected to a very small piece of iron that is then positioned between a magnet and coil inside the cartridge body, but the physics are the same (there are still other types that work on somewhat different principles, but they're less common). The result is that current and voltage are generated by the cartridge, which is passed then to a special equalizer called a phono stage (or phono corrector, or RIAA corrector), then to an amp, then speakers. The cartridge generates electricity from motion. The motion is created by the record groove wiggling the stylus. If the record isn't spinning, the stylus just sits there, and no electrical output from the cartridge is generated. Since the mechanical energy for the groove-to-stylus motion comes from the fact that the record is spinning, the source of the mechanical energy must be the turntable motor. In effect, the turntable converts the mechanical energy of its motor to the electrical energy of the stylus output.
