Researchers propose that experiencing and manipulating physical principles through objects allows young children to formulate scientific intuitions that may serve as precursors to learning in STEM subjects. This may be especially true when children discover these physical principles through object affordances during play. The present study investigated preschoolers' spontaneous explorations of physical phenomena during their object play experiences. It consisted of biweekly naturalistic observations of 20 children's free play, carried out over 8 weeks in two northeastern United States preschools. Results demonstrated that children encountered a variety of physical concepts, including magnetism, forces, energy, tension, friction, and simple machines, as they engaged in spatial-mathematical activities, planned and executed play sequences, problem solved, and explored with objects available in their classrooms. The findings offer insights into the physical phenomena available to children through object play and how these opportunities can be used to support children in reasoning about the physical world.