What is the bow?
Your bow is a wooden or fiberglass stick that has horsehair stretched on it, kept tautly. If your bow’s stick is wood, it is usually one of the following woods:
Typically, the black parts of the bow are plastic or ebony wood. The screw is metal. Sometimes there is mother-of-pearl on the frog (the dot on the frog) and sometimes that’s plastic. Take also a look at this video about cheap and expensive bows:
The hair, which is white horsehair, has rosin applied to it that makes the normally smooth horsehair sticky. Rosin’s stickiness is what makes the hair create the violin’s characteristic sound when it is drawn across the strings.