In studying Newton's laws, most teachers expect their students to be able to construct a free-body diagram that shows each of the forces that act on an object whose motion they want students to analyze. However, many students frequently cannot identify the correct number of forces that act on the object, or, having decided that a particular force should be added to the diagram, they cannot accurately identify what object exerts that force. In addition, many students have difficulty implementing Newton's third law and correctly identifying action-reaction pairs of forces as well as internal and external forces. In general students do not have an organized process for creating an abstract free-body diagram given a concrete physical situation. They make educated guesses without any way of knowing if what they have done is correct. The purpose of this article is to describe a tool that has been found to be valuable in helping students address each of these problems.
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Lou Turner; System Schemas. Phys. Teach. 1 October 2003; 41 (7): 404–408. https://doi.org/10.1119/1.1616480
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