The Pencil and Plywood demonstration is one of our most popular and dramatic illustrations of the principles of mechanics. We’ve all seeing experiments with collisions, but this one has some surprising results.

 In this demonstration, we have a long brass tube, and at the end is a chamber with a vise. We put a small piece of plywood in the vise. Then we put a pencil in the far end of the brass tube, and attach a fire extinguisher to it. When we release gas from the fire extinguisher, the force from the gas rapidly accelerates the pencil down the tube. The pencil flies through the tube at high speed, comes out the open end, and slams into the plywood.

When the pencil strikes the plywood, by Newton’s principal of inertia, it tends to keep moving unless an outside force (from the plywood) changes that motion. It’s moving very fast, though, and by the time the plywood has exerted enough force to stop it, the pencil has blasted partway through the wood! This is an exciting way to illustrate forces and inertia, though some have pointed out that it’s also a waste of a perfectly good #3 pencil.

 Today, we’re going to take a closer look at it, with some measurements you can make at home to complete the experiment. Read more at this link!