From Balancing a Stick to Tightrope Walking: How Added Mass Influences the Act of Balancing

Abstract

Physics-related tricks that use simple everyday materials, which many children attempt, are often entertaining, memorable, and motivate their interest to physics. One example is balancing a stick on a fingertip or open palm (Fig. 1). To balance a stick, there are two important aspects that must be considered: i) the rotational dynamics of the stick as it falls to one side, while the finger (pivot) is stationary, and ii) the human response to this process. The latter aspect is linked with feedback control theory, human time-delayed response, gaze location (where a person looks at the stick), and the limitations of the human nervous system, and is rather complicated. However, controlling the balancing and the corresponding human reaction depends on the rotational dynamics of the stick falling. Analysis of the rotational dynamics are a process suitable for consideration in introductory physics courses.