CTS Guide: Forces Between Objects, pp 178-179- Section IV Research Summaries

Forces on Objects at Rest

• Students tend to distinguish between active objects and objects that support or block or otherwise act passively, such as a table. Students tend to recognize the active actions as forces but often do not consider passive actions to be forces. Teaching students to integrate the concept of passive support into the broader concept of force is challenging, even at the high school level. Some students believe that if a body is not moving, there is no force acting on it (AAAS 2009).

• Students have difficulty understanding that all interactions involve equal forces acting in opposite directions on the separate, interacting bodies. They tend to believe that animate objects (like a person’s hands) can exert forces whereas inanimate objects (like tables) cannot. Some research has shown that teaching high school students to seek consistent explanations for why objects are at rest can help them understand that both “active” and “passive” objects exert forces. Showing students that apparently rigid or supporting objects actually deform might also help them to understand the at-rest condition (AAAS 2009).

• Using the example of a book on a table, many students, including high school students, merely think of the table as being in the way, rather than exerting a force. Students generally appear to think of force as a property of a single object rather than as a feature of interaction between two objects (Driver et al. 1994).