Grades 3–5 · Everyday Life
How does rough sandpaper make wood smoother?
Sandpaper feels rough because hard abrasive grains are attached to its backing. Those tiny grains have edges and points. As the paper moves over wood, the points can cut or scrape away small pieces.
In the diagramHard grain edges remove wood from high spotssandpaper movementsmall removed pieces + smaller remaining scratchesEnlarged grains remove material and leave scratches.
High spots on an uneven wooden surface meet the abrasive first. Repeated movement gradually removes material there. The wood does not become smooth because roughness is added; it becomes smoother as uneven material is taken away.
The grains also leave scratches of their own. Larger grains usually remove material quickly but leave deeper marks. Finer grains make smaller scratches, which can make the surface feel smoother after the larger unevenness has gone.
The result depends on the abrasive, the wood and how the surfaces meet. A sheet can also become clogged or worn. Its useful action comes from many small cutting contacts acting together across the moving surface.
About this explanation
Starting knowledge: Know that wood has uneven surfaces and that a harder edge can remove small pieces of another material.
Sources
- 3M — Sandpaper Sheets and Rolls