We investigate the role of physical properties in determining how people select objects for use in physical activities. W e propose a geometric model in which dimensions represent properties relevant to the goals of the activity and objects occur as points in this property space. A n object's proximity to an ideal value on each property is additively combined across properties to produce a measure of the usefulness of the object for that activity. W e report an experiment that shows that this ideal-point model successfully describes how people select an object for use in a physical activity by using physical properties as an intermediary factor. This model is derived from models of preference choice in which an individual selects objects that he or she prefers.