Most people find the sound of fingernails scraping on a chalkboard to be one of the most nails-on-a-chalkboard-y sounds imaginable. It’s a sound that’s often used to indicate discomfort, or to get someone’s attention in a very dramatic way.
The sound of fingernails scraping on a chalkboard is actually caused by two things: the physical properties of fingernails and chalkboards, and the way our brains process sound.
Fingernails are made of keratin, which is a tough, but flexible protein. Chalkboards, on the other hand, are usually made of slate, which is a type of metamorphic rock. Both materials are quite hard, which is why the sound of fingernails on a chalkboard is so sharp and grating.
When you scrape your fingernails along a chalkboard, the keratin fibers of your nails catch on the surface of the slate. As your nails move, they snag on the slate and pull at the fibers. This produces a vibration that travels through the air and into your ear.
Your brain is very good at picking up on these types of vibrations and translating them into sound. In fact, your brain is so good at it that the sound of fingernails scraping on a chalkboard seems much louder than it actually is.
So why does the sound of fingernails scraping on a chalkboard bother us so much?
There are a few theories. One is that the sound is simply too loud and jarring for our brains to handle. Another theory is that the sound is similar to that of nails scratching on a chalkboard, which is a sound that we associate with nails on a chalkboard.
Whatever the reason, the sound of fingernails scraping on a chalkboard is definitely one of the most nails-on-a-chalkboard-y sounds out there.