What is the difference between a piano and a guitar?

A piano is a, usually large, percussive instrument where the player sits down facing the instrument and uses their fingers to press down on keys that cause a hammer to strike strings of varying tone. There are pedals on a piano that allow the strings to sustain their vibrations or dampen the strings to create a quieter playing effect. A guitar is a hand held instrument where the player uses one hand to pick or strum the strings and the other hand to press down on the strings in various positions in order to change the tone of the string.