It is made of horsehair and wood and cat gut.
The vioin has four strings. Each string is similar in the sense that each has a treble pitch.The first string is usually made from steel. The second and third strings are made from catgut. Despite the name of 'catgut' this is actually derived from the intestines of a sheep, but is still termed 'catgut'. Synthetic materials are not generally used as an alternative.
The fourth string is also made of catgut but then it is usually covered with a very fine film of silver or copper wire.
The violin is played using a bow which consists of more than 150 horsehairs. When the bow is drawn across the violin strings, the rough texture of the horsehair causes the strings to vibrate, each with a slightly different note, depending where it is touched, the finger movements involved and which string it is and how it has been coated or whether it is pure 'catgut'.