We report on an investigation of student understanding of rigid body dynamics in which we
asked students in introductory calculus-based physics to compare the translational motions of
identical rigid bodies subject to forces that differed only in the point of contact at which they
were applied. There was a widespread tendency to claim that forces that cause rotational motion
have a diminished effect on translational motion. A series of related problems was developed to
examine whether similar errors would be made in other contexts, and interviews were conducted
to probe student thinking in greater depth. In this paper, we describe the results of our
investigation and also describe a series of different interventions that culminated in the
development of a tutorial that improves student ability to apply Newton’s second law to rotating
rigid bodies