NonCommercial-ShareAlike 4.0 International
https://creativecommons.org/licenses/by-nc-sa/4.0/
Surface roughness
Surfaces that appear smooth visually and when touched, for example the mirror above, are not in reality - there is a fine scale roughness. Surface roughness can be quantified using a stylus profilometer, where a fine stylus is dragged across the surface. Inevitably, this will produce some smoothing of the true profile because of the finite dimensions of the stylus tip.
Select the stylus size to see how this affects the apparent surface profile:
Large stylus
The animation above shows the stylus scanning over the surface.
Click next to see the recorded surface profile.
Fine stylus
The animation above shows the stylus scanning over the surface.
Click next to see the recorded surface profile.
Profile due to large stylus
If the needle is too large the surface appears perfectly smooth.
Apparent topology:
This stylus size is one extreme. The other extreme gives a perfectly smooth surface topology. In between these extremes you will see the surface is not perfectly flat but that the measured profile will be more smooth than the true profile.
Profile due to fine stylus
The stylus is now fine enough to record the surface roughness accurately.
Apparent topology matches the actual topology:
This stylus size is one extreme. The other extreme, an ideal stylus, gives the exact surface topology. In between these extremes you will see the surface is not perfectly flat but that the measured profile will be more smooth than the true profile