One area explored in the second (in-depth) phase of the Learning in Science Project was "children's science," defined as views of the world and the meanings for words that children have and bring with them to science lessons. The inquiry reported focuses on problems/difficulties of learning about the concept of "force" through analysis and comparison of the nature and place of this concept in both "children's science" and "scientist's science." Data were obtained by the "interview-about-instances" procedure in which students were shown diagrams on cards which represented different instances (exemplars) and non-instances (non-exemplars) of the concept. The first section considers children's views of forces, analyzing them in terms of some common aspects of children's science identified from a variety of studies. These studies indicate that children are influenced by everyday use of the word and tend to have a human-centered view of the world and endow objects with human characteristics or endow abstract ideas with an almost material existence. The second section considers how a scientist's conception of force differs from that understood by children, followed by views of students who have been taught physics (including 100 college students). Interview cards used and a summary of other studies on force are included in appendices. (JN)