Students often fail to see the kinematical constraint of a string connecting two accelerating objects.

"Research as a guide for teaching introductory mechanics: An illustration in the context of the Atwood's machine," L.C. McDermott, P. S. Shaffer, and M. D. Sommers, Am. J. Phys. 62, 46-55 (1994).

Students who do well in quantitative problem solving have difficulties with purely conceptal problems.

"Student understanding of the work-energy and impulse-momentum theorems," R. A. Lawson and L. C. McDermott, Am. J. Phys. 55, 811-817 (1987).

 

Students fail to see acceleration as the ratio Dv/Dt.

"Investigation of student understanding of the concept of acceleration in one dimension," D.E. Trowbridge and L. C. McDermott, Am. J. Phys. 49, 242-253 (1981).

Students use compensation arguments to incorrectly solve conceptual problems.

"Student understanding of the work-energy and impulse-momentum theorems," R. A. Lawson and L. C. McDermott, Am. J. Phys. 55, 811-817 (1987).