# How hot does the tip of a pencil get while writing?

When writing with a pencil, there seems to be quite a lot of friction - which seems like it would induce heat.

How hot would the tip of a #2 pencil get writing on normal copy paper?

• Graphite is both a good lubricant and a good thermal conductor, so what little heat is generated would probably not stay localized and would be spread among the entire pencil lead, heavily diluting the extra thermal energy (though that picture will be somewhat affected by the amount of clay used in the pencil lead). I'll be surprised if anyone manages to pull some figures, though. – Nicolau Saker Neto Jun 2 '13 at 2:53
• The heat from friction will almost immediately dissipate through the pencil lead due to graphite's high thermal conductivity, but in making a mark on a piece of paper, work has to be done to separate the graphite planes and leave a mark. If writing occurs close to thermodynamic equilibrium, the amount of heat released should be readily computable from data on surface energy. – Chay Paterson Jun 2 '13 at 11:21
• I'll see if I can find some data on surface energy of graphite in the literature and have a go! It's relevant to CVD synthesis of graphene, so there must be something in the literature. – Chay Paterson Jun 2 '13 at 20:32

Graphite (pencil "lead") is an allotrope of carbon that occurs in layers of carbons arranged into hexagons, tessellating the plane. Each carbon is $sp^2$ bonded and each layer is one atom thick. The bonds holding the carbons in one plane together are incredibly strong, uniform covalent bonds of strength ~1.33, and the carbons are in a very stable hexagonal arrangement. These bonds are incredibly difficult to break, hence graphite's extraordinarily high melting point (several thousand kelvins).