Surface roughness is a measure of the texture of a surface. It is quantified by the vertical deviations of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small the surface is smooth. The measurement of surface roughness is given as either Ra (Arithmetic average) or RMS (Root Mean Square).
Roughness plays an important role in determining how a real object will interact with its environment. Rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces. Roughness is often a good predictor of the performance of a mechanical component, since irregularities in the surface may form nucleation sites for cracks or corrosion.
PhotoMetrics uses a Scanning Probe Microscope to measure the surface roughness of samples from microns to Ångstroms.