Bow (music)
The wood used for good quality bows is usually pernambuco wood from Brazil.  Some bows nowadays are made from carbon fiber.  They are often cheaper and still of very good quality.  The bow has to be slightly curved so that it straightens out a bit as the hairs are tightened (this is like the bow of ‘bow and arrow’ where letting go of the tension of the bent bow makes the arrow fly off).