A small device with several moving parts helps me to hold my violin. It is a shoulder rest, and it attaches to the bottom of the violin near the base to fill the space between my shoulder and chin and keep the violin in place, leaving my left hand free to play notes rather than support the weight of the instrument. The shoulder rest incorporates simple machines to make it an adjustable device, allowing for differences in sizes of violin bodies and human bodies.
“Machines” in the Life Science Library says the Greek engineer Hero of Alexandria, about the time of Christ, listed five basic machines: the lever, wheel and axle, pulley, wedge and inclined plane, and screw, which form the basis of all other machines. “... [T]hese tools are viewed as ‘simple machines’ — detachable extensions of the human body that, in the main, supplement the function of arms,” says “Machines.”
A shoulder rest is a piece of curved wood or plastic shaped to match a person’s shoulder and the curve of the violin body, and two forks extend down from the ends to allow it to clamp to the violin body and provide the necessary height. A screw and nut hold an end piece on each end, that piece having several holes for width adjustment. The fork attaches to the end piece by a screw in a drum, which rotates so the fork can be folded down for storage, and the screw allows for height adjustment. It also allows the fork to rotate to fit the curve of the violin bout. This is probably all Greek unless you’re an engineer or a violinist, and because I’m not an engineer and not versed in describing physical objects, I refer the reader to the Kun Shoulder Rest website, kunrest.com.
The violin itself is a delicate, graceful, carefully shaped wooden box designed to project the sound of the strings. Those four strings run from wooden pegs in the peg box to the tailpiece. They are wrapped around the pegs, each peg acting as a windlass that winds the string around itself, the end of the string inserted in a hole through the diameter of the peg, allowing the player to tighten the string to pitch and keep it there. The wider handles of the peg act as levers that allow the player to turn the peg.
The base of the string runs either through a hole in the tailpiece and a loop in the string end or is hooked to a fine tuner, which is a hook to accept the string loop and a screw adjuster to change tension, and thus pitch. Violins have at least one fine tuner, and many have four, one for each string.
The bow is a slightly concave length of wood with horsehair attached, and the player tightens the hair by turning a screw in the lower end of the bow. The bow is a lever, and playing continuously changes the placement of the bow as the it travels back and forth from tip to frog and rocks from string to string. The hair grabs the strings, using rosin for friction, just enough to make good tone, not too much that it prevents travel. A bow with new hair, before adding rosin, has little traction and slides across strings, making even a good player sound like a beginner, although a good player knows enough to apply copious quantities of rosin to new hair.
I’m a string musician, not an engineer, so I apologize to you engineers for my inaccurate terminology and analysis. It’s enough for me to produce tolerable sound from an instrument that can easily degenerate in tone to caterwauling. But I appreciate the complex craft and engineering that have developed over the centuries to create this instrument, whose absurdly difficult technique can drive me daft and others out of the room.