Physics I Laboratory Grading Rubric for Written Reports (5 required beyond Lab #1).  Each experiment will be tallied for a total of 100 points.   Fall 2011


DESCRIPTION OF THE EXPERIMENT.  30 points.

Clearly identifies the purpose of the experiment.  This should be written in clear, succinct prose.  Use first person or third person, but should be consistent

 

EXPERIMENTAL RESULTS.  40 points.

 

DISCUSSION OF THE RESULTS (this is often the most difficult part of the report).

30 points.


SUGGESTIONS FOR STYLE.

The style elements are not as "ironclad" in the grading rubric, but attention to the style suggested here should help make more meaningful and readable reports and should help students better communicate in their chosen professions.

A.  Organization when several smaller experiments are involved.

Many physics laboratories involve more than one experiment that are related.   As an example, the first laboratory involves measuring the speed of a ball that is tossed between two people as well as the motion of a bowling ball as it rolls along a hallway.  It is much better to complete the write-up (description, results, discussion) for the first part of the lab before beginning to discuss the 2nd part of the lab.  It makes reading (as well as writing) the reports easier if the report is organized to present the complete report of the first experiment (description, results, and discussion) before introducing the second experiment.  Beginning students are often tempted to describe the first experiment followed by a description of the second experiment before any results are presented.  This breaks the reader's train of thought - especially when the introduction is so well done prompting the reader to be anxious to see the results - only to have the thought process interrupted by a different experiment.  Thus, when appropriate, reports should be organized to complete the results and discussion of the first experiment before introdcing the second experiment.  A final discussion tying all experiments together is also appropriate with multiple experiments.

B.  Avoid round-off errors in intermediate calculations.

The best way to show this is an example.  Suppose a student measures the sides of a right triangle to be 4.58 cm and 3.28 cm.  See the diagram.  Note that both of these measurements have 3 significant digits.  A student does the calculation correctly on a calculator and presents the result as 5.633364891430 cm.  Here the student will have points docked for significant digit violations.  This 13 digit result should be rounded to no more than three significant digits (5.63 cm) to avoid the egregious significant digits error and earn credit for the correct result.

Having been so severely reprimanded of the significant digits mistake, the student typically tries another tactic to avoid excess digits.  In calculating the squares in the Pathegorean formula, the student rounds (4.58 cm) 2 =  (20.97640000000 cm2  = 21.0 cm2).   (3.28 cm) 2 =  (10.75840000000 cm2 = 10.8 cm2) .   The student then takes the square root of the sum of the "rounded squares" to be 5.64 cm:



Notice that the student obtained a small error (5.64 cm) rather than 5.63 cm.  This error seems small and insignificant, but represents a subtle error due to rounding-off intermediate calculation results.  When calculations are more complicated than this simple example, several round-off errors may accumulate and become significant.  The best method is to use and keep the full internal precision of the calculator for intermediate calculations, save rounding until the end.  If intermediate results need to be written down and re-entered, they should contain one more significant digit than needed for the result.  Also, don't forget the rules for rounding:  5.635 to 5.639 all round to 5.64.

C.  Use computer tools for equations and line drawings.

Although it is not required that the students use the tools of computer word processors to produce equations and line drawings (it is satisfactory that these be done by hand) the gain in readability and appearance is remarkable.  It takes a little longer to use these tools, but once they are completed, there is much less tendency to forget to hand-draw the equations and diagrams when turning in the report.  Be sure to install the Equation Editor if you are using MS Office.  If you do not have MS Word for your own computer  you may purchase MS Office 2007 for about $86.00 including postage from www.scholarbuys.com.  An even lower cost alternative is to use Open Office (free from Openoffice.org 150 MB download).  Open Office works on any platform.  If a student includes electronic equations and line drawings with the final report, significant paper may be saved by submitting the lab report electronically as an e-mail attachment.