The science behind drawing and erasing

What are the different scientific phenomena that go into the act of using a pencil and an eraser to remove pencil marks?

OBJECTIVES

• How does the pencil leave a mark where it rubs a surface?

• Why and how is an eraser able to remove the traces of a pencil?

MATERIALS NEEDED

• x1 Pencil (not coloured)

• x1 Eraser

Process

Drawing

Fun Fact: Pencil leads were never actually made of the element 'Lead', however, they are made of a non-toxic material called 'graphite' (mixed with clay and formed into long, thin pencil lead).

Like I mentioned before, the lead of a pencil is made of tiny graphite molecules which contain 6 carbon atoms in a hexagonal structure, as shown in the figure below.

The graphite molecules, as you can see, are stacked in layers. These layers can slide over each other.

So, when a pencil lead makes contact with paper, the lead allows graphite molecules to slip onto the paper, leaving a mark on its trail.

Erasing

• Erasers work because of FRICTION.

Friction is the force of resistance to motion of one object moving against another.

• The modern eraser is usually made of a mix of abrasives such as fine pumice, a rubbery matrix such as synthetic rubber or vinyl.

• When you rub an eraser on a pencil mark, the abrasives in the eraser gently scratch the surface fibres of the paper to loosen the graphite particles.

• Moreover, the rubbing motion causes friction, which produces heat. The heat helps the rubber become sticky enough to hold onto the graphite particles.

• Small pieces of the rubber combined with graphite get left behind as a result.