Because
Many different materials: gut, nylon, steel, chromesteel, copper, bronze.
Steel. I think. The can be made of steel, aluminum, or copper.
Copper is unique chemical element.
A 10p coin in the UK is made of a combination of metals, primarily copper-plated steel. It consists of 75% copper and 25% nickel. The outer layer is made of copper and the inner core is made of steel.
The Iraqi coins made for general use since 1960 are made of nickel, copper-nickel, stainless steel, copper plated steel and nickel plated steel.
to make the string make a low pitch sound
Irish (Eire) "copper" decimal coins issued from 1971 to 1988 were made from bronze consisting of about 97% copper, the remainder being tin and zinc. Irish (Eire) "copper" decimal coins issued from 1988 to 2001 were made from copper plated steel.
lead, copper, steel
Copper is a better conductor of heat than steel.
American nickels are made of 75% copper and 25% nickel Canadian nickels used to be pure nickel but are now made out of steel.
A guitar string is typically made of steel or nylon, depending on the type of guitar and the desired sound.
Usually from metals such as steel and nickel. Like pure steel, nickel wrapped steel, pure steel etc