Abstract
Changing mass phenomena like the motion of a falling chain, the behaviour
of a falling elastic bar or spring, and the motion of a bungee jumper surprise
many a physicist. In this article we discuss the first phase of bungee jumping,
when the bungee jumper falls, but the bungee rope is still slack. In
instructional material this phase is often considered a free fall, but when the
mass of the bungee rope is taken into account, the bungee jumper reaches
acceleration greater than g. This result is contrary to the usual experience
with free falling objects and therefore hard to believe for many a person, even
an experienced physicist. It is often a starting point for heated discussions
about the quality of the experiments and the physics knowledge of the
experimentalist, or it may even prompt complaints about the quality of
current physics education. But experiments do reveal the truth and students
can do them supported by information and communication technology (ICT)
tools. We report on a research project done by secondary school students and
use their work to discuss how measurements with sensors, video analysis of
self-recorded high-speed video clips and computer modelling allow study of
the physics of bungee jumping.