Difference between flatness and surface roughness

Question

Accepted Answer

Flatness refers to the deviation of a surface from a perfect plane, while surface roughness refers to the texture of the surface.

Flatness is a measure of how level a surface is, while surface roughness is a measure of how bumpy or irregular the surface is.
Flatness is typically measured using a straightedge or surface plate, while surface roughness is measured using instruments like profilometers or roughness testers.
Flatness is important in applications where two surfaces need to mate perfectly, while surface roughness is important in applications where friction or wear is a concern.
Examples of flatness include the surface of a table or a machined metal part, while examples of surface roughness include the texture of sandpaper or the surface of a golf ball.

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