An acoustic grand piano is the classic piano as we have known it for many years. It has strings and an ingenious action mechanism which causes felted hammer heads to strike the strings. The hammer heads are set in motion by pressing the pianos keys. When the keys are pressed, the hammers cause the strings to vibrate, and these vibrations are transferred to the soundboard, creating a wonderful sound.
Each key has its own hammer and string to create a tone. The keyboard is sensitive to touch, which means that pressing the key softly will create a softer tone and pressing the key hard will create a louder tone. The piano's keyboard is sometimes also called the clavier. In total, the keyboard consists of 88 keys (52 white and 36 black ones).
Acoustic pianos have two or three pedals. The left pedal, when pressed, causes the instrument's tones to sound more softly. The right pedal, when pressed, makes a tone sound on after it has been played. The middle pedal's function varies, depending on the type of upright or grand piano you're dealing with.
An acoustic instrument needs to be tuned several times a year. The piano's string tension increases or decreases, because the wooden and metal parts expand and shrink. By tuning a piano, its proper string tension is restored. Tuning is done by turning the tuning pins.