Riamh
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Why do matt surfaces have cavities?
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Motorbiker
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(Original post by Riamh)
Why do matt surfaces have cavities?

Moved this question to the physics Study help forum for you.
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uberteknik
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(Original post by Riamh)
Why do matt surfaces have cavities?
Perhaps the question should be asked the other way around: Why do surfaces with cavities have a matt appearance?

There are two separate things that need to be considered: the physics of the light interacting with a surface, and, the human perception of shiny and matt surfaces.

When a wave-front of light reaches a surface of material, the light will interact in three ways: absorption, where the atoms at the surface of the material become more agitated (the material heats up); reflection, where the incident light changes direction (bounces) away from the surface dependent on the incident angle; refraction, the incident light changes direction but continues on through the material and again dependent on the density of the material and the angle of incidence.

If a surface comprises cavities, pits, bumps etc. these will cause the incident light to scatter in different directions as well as refract in different directions. The surface area of the material presented to the incoming light is also greater, so more absorption occurs as well.

The human eye registers incoming light to allow the brain to form an image of the world around us. We learn to recognise objects from the incident light on our eyes because that light itself was reflected off an object and formed a unique pattern.

Human perception of shiny and matt surfaces is dependent on whether the visual information within an image (pattern) is largely retained or destroyed.

When we view a shiny surface, we are looking at the reflection of light off that surface. The visual information (pattern of light) reflected from a shiny surface is largely retained and can therefore be recognised by the brain. i.e. we see the reflections in a mirror because the reflected light contains enough of the original incident pattern of light such that the brain recognises the pattern of reflection.

With a matt surface, the reflection of light is scattered and random. Any visual information from the original incident light is lost and the brain can no longer decipher the reflection as something it recognises. We register the lack of visual cues and label the perception as a matt surface.
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