Piano Tuning

Why do pianos need to be regularly tuned ?

A piano is a stringed instrument made of wood, felt, and other materials that physically expand and contract over time due to changes in environmental temperature and humidity.  This constant flux of materials continually pushes and pulls against the strings which deliver the beautiful sound of the piano of which we are accustomed to hearing.  When the strings are physically stretched, the precise tension at which they are set by your piano tuner changes, resulting in a change in pitch that we hear from the strings, rendering the piano "out of tune."  Additionally, simply playing the piano will stretch the strings as the hammers strike them, producing more change in the tone we hear from the piano.  The louder the pianist plays, the harder the hammers strike the strings, thus the faster the piano falls out of tune.