Does a pencil float on avgas?
Good question.
According to
How pencil is made - material, manufacture, making, history, used, processing, steps, product, machine, Raw Materials, The Manufacturing Process of pencil, Colored pencils, Quaility Control, pencils are typically made from Cedar wood. Dry Cedar has a SG of .38 (
Specific Gravity Of Wood Table).
The SG of the graphite core is less readily available, but is apparently between 1.9 and 2.3. (
Graphite: The mineral Graphite information and pictures)
The thickness of a pencil is 6mm (radius 3mm) so by a first approximation the cut-through area is 3^2*pi = 28.3 mm2. The lead core has a diameter of 2mm (radius 1mm) so that area is 3.14 mm2.
This means the worst-case SG of the pencil is approximately ( (.38 * (28.3-3.14)) + (2.3 * 3.14) ) / 28.3 = .59. The SG of avgas is .72 so the pencil should float. But this does not take into account the weight of the varnish and a possible eraser. Or what happens when the wood soaks up the avgas, or the effects of a potential chemical reaction between the graphite core and the avgas. Or the fact that if you sharpen the pencil, you remove relatively more wood than graphite core so the SG goes up.
So I would not automatically assume a pencil floats in avgas.