The Piano

The piano is a percussion instrument
When you press a note on the keyboard, a hammer strikes the string that produces the note. Since sound comes from something hitting another object, the piano is a percussion instrument. It's a percussion instrument where instead of striking a drum, you're striking a string.

Each string usually holds around 168 pounds of tension. The total tension of most standard pianos is around 18-20 tons. Some of the largest grand pianos hold up to 30 tons of tension!
Up until the 1950s, piano keys were made from elephant tusks. Today, in order to protect and preserve elephants, most piano keys are made from plastic.