A tuning fork is a two-pronged metal tool that produces a clear, steady musical note when you strike it. The fork is shaped like a Y, and when you tap it against something or flick it with your finger, the two prongs vibrate back and forth incredibly fast, creating a tone that hangs in the air.

Musicians use tuning forks to tune their instruments. A common tuning fork produces the note A at 440 vibrations per second, which serves as a reference point. If you strike the fork and hold it near your ear, or touch its base to a wooden surface like a guitar or table, you'll hear that A note. A guitarist can then adjust their strings to match.

Tuning forks are also useful in science classrooms for studying sound waves and vibrations. Because they produce a very clear tone with few extra sounds, they're helpful for experiments about how sound travels through air, water, and solid objects.

Before tuning forks, musicians used pitch pipes or tuned to whatever instrument was handy, which meant orchestras often sounded slightly off. The tuning fork gave musicians something consistent and portable, something that would produce the same note every time, anywhere in the world.