The piano is one of the most recognisable musical instruments and one of the most uniquitous becuase of its unique tibre, its huge range, its dynamic range and its harmonic capabilities. Becuase of this it is difficult to imagine a musical landscape which doesn't include the instrument. However, the piano in its modern guise is a relativley recent invention; composers such as Mozart and Bach would not reconise the modern Grand piano, for example.
All pianos produce their sound by felt hammers striking steel strings within the instrument itself. When a pianist presses down a key a hammer strikes the strings tuned to that note which vibrate until the key is released. When the key is released a damper stops the note by preventing the vibrations continuing. This system, invented in the early 18th century was a departure from other keyboard instruments whose strings were plucked rather than struck. The advantage of this new mechanism was that keyboard players, for the first time, had a huge dynamic range available to them as controlling the speed at which the hammer hits the strings determines how loud the resulting note is.
The next innovation in the evolution of the piano was the invention in the 19th century of the iron-frame. An iron-frame, as opposed to a wooden one, allowed longer strings to be strung at gerater tensions. This had two advantages; longer strings allow for a greater purity of sound, and greater tension means a more powerful sound can be generated. It is this invention that gave composers the ability to compose ever more virtuosic - and powerful - music for the instrument.
The piano's colourful timbre is further enhanced by the use of pedals. Most pianos, whether Grand or upright, have a soft pedal and a sustain pedal. The soft pedal, through mechanisms which differ depending on the type of piano, means the piano produces a softer sound with a slightly different timbre. The sustain pedal (the pedal most often used by pianists) prevents the dampers from stopping the note once a key has been released.