[chris (OP)]

Sometimes, when cutting something on a plate, the knife or fork slips; this is accompanied by a high-pitched scraping or screeching sound that makes some people shudder.

What is the source of that sound?

[Colin2B]

What is the source of that sound?

It’s caused by a friction phenomenon called slip-stick. The knife blade (also fork tines, fingernails on blackboard etc) alternately slips and sticks across the surface causing vibration, amplified by the surface.
The nerve racking sound is when a lot of the power is in the very sensitive range of hearing (around 3-4kHz) and contains a lot of discordant harmonics.

[chris (OP)]

The knife blade (also fork tines, fingernails on blackboard etc) alternately slips and sticks across the surface causing vibration, amplified by the surface.

Thanks.

Why that surface in particular, and why at that frequency?

[evan_au]

A lot of stick/slip phenomena (including earthquakes) have a chaotic nature, so the point at which they stick or slip is random.

This produces a wideband noise, that often sends chills up your back.
- This is the case of a scream from a terrified human
- In the case of the violin, the periodic structure of the horse-hair bow allows an expert to produce harmonic sounds. But an amateur often produces a chaotic shriek.
- In the case of ceramics, they are very hard, with a high speed of sound; I would expect this to produce higher frequencies.

[chris (OP)]

- In the case of ceramics, they are very hard, with a high speed of sound; I would expect this to produce higher frequencies.

Thanks; this is the crucial detail I am interested in. What is the relationship between the hardness, speed of sound and resonant frequency?

[Colin2B]

- In the case of ceramics, they are very hard, with a high speed of sound; I would expect this to produce higher frequencies.

Thanks; this is the crucial detail I am interested in. What is the relationship between the hardness, speed of sound and resonant frequency?

I seem to remember some research suggesting it isn’t the plate/blackboard that produces the sound but the knife, fork or chalk and its contact shear area + vibrating length. I have it marked somewhere, will try to find it.

[evan_au]

A metal knife is also much harder than a fingernail or chalk, so it will tend to vibrate at a higher frequency.
- The wide blade will act as a loudspeaker, coupling energy into the air more effectively

A scraping knife can be considered a cantilevered beam, excited by the stick/slip friction against the plate.
- The natural frequencies of oscillation of a cantilevered beam involve hyperbolic functions like COSH, so they are not "harmonic" frequencies in the sense that a vibrating string produces frequencies that are multiples of a fundamental
- Factors which affect the frequency include the mass per unit length and the rigidity of the material (which tends to return the distorted material to the neutral position)
See: https://en.wikipedia.org/wiki/Euler%E2%80%93Bernoulli_beam_theory#Dynamic_beam_equation

[kurtmhilliard]

Sometimes, when cutting something on a plate, the knife or fork slips; this is accompanied by a high-pitched scraping or screeching sound that makes some people shudder.
What is the source of that sound?

I think it's the sound of excitement caused by fear.

[chris (OP)]

A metal knife is also much harder than a fingernail or chalk, so it will tend to vibrate at a higher frequency.
- The wide blade will act as a loudspeaker, coupling energy into the air more effectively

Ah, so it's the knife resonating, not the plate?

[Colin2B]

Ah, so it's the knife resonating, not the plate?

Yes

Thanks; this is the crucial detail I am interested in. What is the relationship between the hardness, speed of sound and resonant frequency?

I seem to remember some research suggesting it isn’t the plate/blackboard that produces the sound but the knife, fork or chalk and its contact shear area + vibrating length. I have it marked somewhere, will try to find it.

Found it, lets see if I can attach it.
Mmm, that failed, will try another way

[Petrochemicals]

A metal knife is also much harder than a fingernail or chalk, so it will tend to vibrate at a higher frequency.
- The wide blade will act as a loudspeaker, coupling energy into the air more effectively

Ah, so it's the knife resonating, not the plate?

You get it with metal on metal too, but i would say that the plate does resonate from my experience, it produces a more tinny sound. One for the experiments at sunday dinner, try dampening the plate chris