Where will a pen fall to?

Abstract

We propose a simple experiment that everybody can carry out just while reading this paper. The only thing we need is a pen or a pencil and a finger. The dynamics of the falling pen, which is in touch with the finger, depends essentially on the initial inclination angle of the long axis of the pen. We point out two different types of trajectories of the falling pen and we investigate initial conditions for each of them to be realized. We write differential equations describing the dynamics of the pen and analyze them both numerically and analytically.