Inventor: John Shore

The tuning for resembles a wishbone and is used to hear the "A" note (the ‘la’). The ‘A’ is the note that is usually used to tune an instrument—the subsequent notes are tuned in accordance with the A note. It was invented by John Shore, Sergeant Trumpeter to the court, in 1711.

When struck against the music stand (which is what orchestra students usually do) or caused to vibrate, the tuning fork resonates at the constant pitch of the ‘A’ note. Of course, the pitch that the tuning fork emits differs depending on the length of the two prongs, with the two nodes near the bend of the U. The note it resonates is usually difficult to hear unless the fork is hold right up to the ear. However, when struck and pressed down on a solid surface (ex., a desk), the surface acts as a soundboard and greatly amplifies the note that the fork resonates.

Picture from:
http://web.media.mit.edu/~clarkson/mas863/tuning.fork.jpg

Sources:

MediaWiki. Tuning fork. 2 Jan. 2004 <http://en.wikipedia.org/wiki/Tuning_fork>.

• This site provided me with information on the invention of the tuning fork, its uses, and how it works.