Demos: 1F-09 Pencil Shoot

A slender dowel rod is placed in the end of a long brass tube whose internal diameter is slightly greater than that of the dowel rod.The hose from a fire extinguisher is attached to the end of the tube. Depressing the handle of the fire extinguisher accelerates the pencil down the tube and impales it in a 1/2-inch sheet of plywood, passing at least half-way through the wood.

Directions: Place the dowel rod in the tube and connect the hose from the fire extinguisher. MAKE SURE THAT THE CONNECTION IS FIRMLY MADE. Strike the handle of the fire extinguisher quickly with the side of your hand to “pulse” it.

Suggestions for Presentation: Hold a piece of the plywood in one hand and the small dowel rod in the other. Ask how one might get the rod through the wood. You might even try hammering it through, showing that large forces may be required to get the dowel rod through the wood.

Note: Although it seems counterintuitive, experience has shown that a flat-ended dowel rod (or unsharpened pencil) goes through more cleanly than a sharpened one.

Applications: Point out how tornadic winds often drive pieces of straw or twigs into tree trunks.

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