An inexpensive, multipurpose physical pendulum

The pendulum is a highly versatile tool for teaching physics. Many special purpose pendula for student experiments have been described.^1–4 In this paper, I describe an inexpensive, multipurpose physical pendulum that can function as both a variable gravity and ballistic pendulum. I designed the apparatus for use in a rotational dynamics unit of the AP Physics C mechanics course. The use of a bike wheel hub pivot allows for low-friction, rugged operation that yields results commensurate with those obtained with much more expensive pendula available on the market (typically $500 per unit⁵), placing these types of experiments within reach of the teacher on a restricted budget.