  Much recent work in physics education research has focused on ontological
metaphors for energy, particularly the substance ontology and its pedagogical
affordances. The concept of negative energy problematizes the substance
ontology for energy, but in many instructional settings, the specific
difficulties around negative energy are outweighed by the general advantages of
the substance ontology. However, we claim that our interdisciplinary setting (a
physics class that builds deep connections to biology and chemistry) leads to a
different set of considerations and conclusions. In a course designed to draw
interdisciplinary connections, the centrality of chemical bond energy in
biology necessitates foregrounding negative energy from the beginning. We argue
that the emphasis on negative energy requires a combination of substance and
location ontologies. The location ontology enables energies both "above" and
"below" zero. We present preliminary student data that illustrate difficulties
in reasoning about negative energy, and the affordances of the location
metaphor.
