Physical geomorphometry is introduced as a specific subfield of geomorphometry, investigating the land surface in terms of the basic principles, practices, and concepts of physics. The interconnected system of geomorphometric energies gives meaning to the summation, difference and ratio of basic geomorphometric variables. This explains the mutual relations of many well-established variables, indexes and equations and enables construction of new indexes expressing land surface (dis)equilibria. Conspicuous analogies between some aspects of physical geomorphometry and general relativity point to the possible wider scientific relevance.