Science of everyday things

Pencil marks are tiny flakes of graphite resting on the paper fibres. An eraser is slightly sticky, so the graphite clings to it more than to the paper, and the crumbs carry it away.

Glue works through two forces. Adhesion makes it cling to each surface it touches, and cohesion holds the glue itself together once it sets. Super glue hardens when it meets traces of water.