The violin, viola, cello and bass fiddle - which make up the strings of the orchestra - are very similar in construction, and all work the same way. A wooden bridge carries the vibrations of the strings into the belly (front) of the instrument, and then the sound is resonated back outward by the smooth back panel. All that wood greatly multiplies the sound volume which is further amplified by the sound holes on the front. And it's all made possible by cellulose, the natural polymer that makes up wood.
In the old days the strings were made out of stuff called catgut, which is a strange name, since it was really from sheep intestine. This stringy stuff is made of tough proteins, and though it was strong and vibrated well, it was very difficult to tune becasue of its sensitivity to weather and temperatre. Now strings are made from steel or nickel wire wound with nickel, silver, or aluminum.
The strings are held taught by a set of wood pegs, and the fingerboard where the player changes the pitch of each string during playing is also wood - more cellulose!
The belly of a violin is usually srpuce, which has a density that vibrates well to amplify sound. (It is also used for piano sound boards) The back resonator is made of maple wood. The glue that holds the whole thing together is a tough adhesive made from horse hide - a form of protein. In all a vioin has about 70 individual parts. That's a lot of glue! Recently a new violin has been invented which is molded from a composite of carbon fiber. The revolutionary new design allows the maker to construct a violin from only 20 parts.
The bow which is used to vibrate the strings has a shaft made from wood which holds a tight arrangement of horsehair. These hairs are formed from protein and actually have a microscopic scaled texture which gives them friction with the violin strings. They are also treated with rosin so that they will have even better friction on the strings to make them vibrate well. The polymers in the bow also have synthetic alternatives. There are composites used for the bowstick which are made from glass fiber or carbon fiber. These materials are light and very strong - well able to handle the tension of the tight bowhairs. Speaking of the hair, there is even synthetic bowhair which can be made form nylon or fiberglass, but it is not considered as good as real horsehiar for playing.
Guitars and their immediate family are constructed quite a bit like the violins. They have a similar wood body and a sound hole in front, not to mention the bridge that carries the sound of the strings into the wood. Guitar bodies can also be made of composites like carbon fiber.
Then there are electric guitars with small solid bodies made from wood like maple. These don't have a normal bridge, but electrical contacts that carry the sounds of the strings out to an amplifier and speakers.
Most guitar strings are made of steel. They are made a lot like piano strings. Some are wire while the lower strings have a wire core with another wire wrapped arouind it. They even make low guitar strings that are wound with flat steel, nickel or silver "ribbon" like violin strings. These metal strings are not polymers. but there is a type of guitar that uses polymer strings.
The classical guitar is different than the steel string acoustic guitar used for pop, folk or country music. You can see the difference in the pictures of both types of guitar. The classical guitar - in the front - looks almost the same but it has nylon strings and the player uses his fingernails rather than a pick to play it. This gives it a much softer harplike sound. Also becasue there is no need for a pick, the classical guitar has no polystyrene pickguard like a steel string guitar. By the way, guitar pics are made from nitrous cellulose - one of the earliest synthetic polymers, and fingernails are a type of protein.
The mandolin and lute are instruments similar to guitars but with differnet body shapes, so - of course - they sound different from guitars.
These instruments have all been around for a long time. In fact J.S. Bach (1685-1750) played the lute and wrote quite a few pieces to be performed on it during the Baroque period. It has a soft sound like a classical guitar because the strings are made of nylon plated with a metal like silver. The mandolin, a "descendant" of the lute, has a more "metallic" sound because it has metal strings wrapped in bronze. The distinct sound it makes is very popular in American folk and Bluegrass music, though traditionally it is used in Italian music. Though the lute and mandolin are made of wood, they - most of all the stringed instruments - keep their ancient gourd-shaped bodies. Lutes, and even some mandolins, are rounded in the back. That's becasue a long time ago these types of stringed instruments were made out of large gourds which were cut in half and hollowed out and covered with the front wood piece. And - like wood - gourds, being plant material, are a form of cellulose.
The banjo has a design unique among stringed instruments and so it also has some interesting polymers in it. The construction came from Africa where someone decided to take the standard gourd back as a resonator, and, instead of a wood front with sound holes as the amplifier, an animal hide "drumhead" was used.
These heads could be made from the skins of gophers, possums, beavers or even cats! The back resonator on a modern banjo is a curved piece of wood - anything from mahogany to rosewood. The neck is made from various woods also - mahogany, maple, rosewood - while the fingerborad is made form ebony. Nowadays some people stll play hide heads on their banjoes, but these are now made from calfskin - a form of protein - and are greatly affected by temperature and weather. They also give a "darker" more mellow sound preferred in more old-timey folk playing. The newer heads - preferred for Bluegrass and other newer styles - are made like modern drumheads, from the plastic polyethylene. They can be clear or frosted with different materials, or even colored. Each treatment of the head causes a slightly different tone.
Like the other members of the string family, the banjo uses a wood bridge (maple and ebony) to transmit the vibration of the strings to the head. Surprisingly, changing the bridge on a banjo is the best way to quickly change the tone. Traditionally the strings were made of gut - like the lute, guitar, fiddle, etc. But now they are metal - phosphor wound in bronze like mandolin strings.
Harps are made in a variety of sizes and sounds with different numbers of strings. The frame of the harp is formed by the column, the soundboard, and the neck, where all the strings are connected and held tight by the tuning pins. All these major parts of the harp are made of wood. The soundboard wich resonates to amplify the sound of the strings is ususally made from spruce, which is supposed to be the best type of wood for soundbards. But the sound board can be made of different kinds of wood as can the rest of the frame.
The strings are traditionally made of sheep gut like most other stringed instruments. Some harps still use gut strings or strings made from synthetic gut. But most harp strings are made of nylon monofilament - like those on a classical guitar, or they can be a nylon core wound with more nylon or a metal such as bronze or silver for a brighter sound. And large pedal harps that need an octave of deep bass strings might have wire wound strings made of steel on the low end. And there are a few folk or lever harps that have all their strings made of wire, a bit like a piano.
One of the best and most important things you can do to care for a string instrument - as with any other instrument - is to keep it in a sturdy case. The case should have a tough outer shell. A simple black student case is made from ABS resin which is very strong. The more complicated models can have shells made from resins or plywood covered with tough nylon like the one in the picture. The various straps and pockets are also made from nylon. The insides of string instrument cases can be made from polyurethane foam cut to the shape of the instrument, or they can be molded to the instrument shape and covered with a soft fabric like felt or velvet.
One important thing that the violin family needs is the regular application of rosin to the bowhair. This slightly sticky stuff coats the hairs and causes friction between the bow and the strings. And without friction, there would be no sound. Rosin is a natural resin made from the sap of pine trees. The sap is boiled and refined and then poured into molds to cool. Each maker of rosin has a different recipe. Some include ingredients like beeswax and other kinds of tree sap to give the rosin certain properties. There are different types of rosin, depending on the time of year the sap is harvested and depending on what other ingredients are added. Darker rosin is more sticky. This is best for the big bass fiddle. The lighter amber-colored rosin is better for violin and viola and the cello. There are also different types that are better for different seasons of the year.
Because things like skin oil, sweat and rosin, which can flake off as a white poweder onto the strings, bow, and body of instruments, the instrument should be cleaned after each practice. The best thing for this is a soft dry cloth. Cotton is a good materal for this. There are also cloths made from microfibers of polyester and nylon. These tiny fibers are good because they are too small and fine to do any damage to the instrument's finish. A cloth should also be used once or twice a year to restore varnish and polish the wood.
Another handy device for string instruments is a humidifier. These help protect the delicate wood and the glue joints from drying out and cracking, especially in the winter. Humidifier can have a plastic casing such as polystyrene or a rubber tube with a foamy spongy polymer inside. The sponge holds the water so that it won't drip out. This is very important since some humidifers are actually kept inside the instrument when it is not being played. They make these for both fiddles and guitars. Another type of humidifier seen here is simply held inside the instrument case with Velcro. So whenever the instrument is not being used, it stays at the proper humidity. You can even get a special guage that measures the humiidty in the case.