  Designing novel cyber-physical systems entails significant, costly physical
experimentation. Simulation tools can enable the virtualization of experiments.
Unfortunately, current tools have shortcomings that limit their utility for
virtual experimentation. Language research can be especially helpful in
addressing many of these problems. As a first step in this direction, we
consider the question of determining what language features are needed to model
cyber-physical systems. Using a series of elementary examples of cyber-physical
systems, we reflect on the extent to which a small, experimental
domain-specific formalism called Acumen suffices for this purpose.
