A Mechanics Baseline Test

By David Hestenes and Malcolm Wells

Published in: The Physics Teacher 30, March 1992, p. 159-166.

 

We have designed a test to assess student understanding of the most basic concepts in mechanics. The test is universal in the sense that it is limited to concepts that should be addressed in introductory physics at any level from high school through Harvard University. We have extensive data on post-instruction scores across the whole range of levels. This provides baseline data for evaluating and comparing the effectiveness of instruction at all levels. For this reason we refer to the test as the Mechanics Baseline.

 

We believe that the best use of the test is for post-instruction evaluation, except for advanced university courses where it may be useful as a pre-instruction placement exam. Of course the self-defeating practice of "teaching to the test" should be avoided, but an examination of the test could help some teachers see where their instruction can be improved.

 

Test Design and Interpretation

The Mechanics Baseline test should be compared with the Force Concept Inventory. The Baseline is the next step above the Inventory in mechanics understanding. Questions on the Inventory were designed to be meaningful to students without formal training in mechanics and to elicit their preconceptions about the subject. In contrast, the Baseline emphasizes concepts that cannot be grasped without formal knowledge about mechanics. The two tests are complementary probes for understanding of the most basic Newtonian concepts. Together they give a fairly complete profile of this understanding.

 

The coverage of basic concepts is quite systematic, although the coverage of Newton’s first and third laws is deliberately thin because these concepts are adequately assessed by the Inventory. Thus, the Inventory and the Baseline are complementary tests in a practical sense

 

For the most part, the Baseline looks like a conventional quantitative, problem-solving test, though its main intent is to assess qualitative understanding.

 

The multiple-choice distracters in the Baseline are not commonsense alternatives as they are in the Inventory, though they include typical student mistakes, which are more often due to deficient understanding than to carelessness. We excluded problems that can be solved by a simple "plug-in" of numbers into a formula.

 

Judged by the low scores of students at all levels, the Baseline is not an easy test. A few of the questions were extracted from Advanced Placement exams, though we found very few AP questions suited to our purpose. Less than a third of the questions require algebraic manipulation or more than one-step reasoning, and advanced concepts such as angular momentum are excluded. Student difficulties with the test appear to stem from real deficiencies in understanding the basic concepts. We aimed for a balanced coverage of these basic concepts, but we made a point of including topics that we know pose the greatest difficulty.