COMMENTS ON WRITING A GOOD LAB REPORT
CHRIS CONKLIN

These comments are derived from feedback I have given to students in the past after having written their first lab reports. They are meant to supplement, but not replace, the advice given in the lab manual. Please consult the lab manual for general guidelines first, then look here for ideas on how to polish. The sections are broken down into Argument,
Technical Style, Use of Physics, and Quantitativeness, to follow the sections of the grading rubric. 1. Argument
This is an area where many students struggle. Remember that a lab report is a lot like a persuasive essay. You want to present what you are trying to prove in your introduction and prediction sections, then present the data in a clear way, then use the data you have presented to show that your prediction was definitively correct or incorrect, or that your results are inconclusive.
In order to present your argument convincingly, a few things have to happen:
(1) You must understand why you are doing the lab.
In a given lab, you will investigate many things on your way through the procedure, but it can be difficult to keep track of what exactly was your goal. Some students say their goal was to investigate more than one thing, which is fine. At the same time, understand that the steps necessary to get to our goal may not be key predictions themselves. For instance, as a part of reaching a conclusion about acceleration, you may need to determine the velocity of an object. If that’s the case, then determining the velocity is not the goal of the lab; it is merely a stepping stone to finding the acceleration. Before you begin writing, make clear in your own mind what the goal of the lab was, and then state it clearly in your report.
(2) You must include all data necessary to draw your conclusions.
This means any (relevant) graphs that you have and any (relevant) measurements you took must be in your lab (with uncertainty of course). A good way to determine if you missing anything is this: if I think you computed something incorrectly and
I wanted to double check your calculation, I should have all the necessary numbers to redo your calculations. I don’t need to see every mathematical step, but I should have enough information to carry out any mathematical steps left out on my own.
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(3) You must not assume the reader knows anything about your lab set-up or procedure.
Students tend to write very good procedure sections. However, I have had many students who start talking about angles and x and y directions without ever drawing a picture or stating a coordinate system. Similarly, many students will state an equation without saying where it came from. If you are using an equation that comes directly from a textbook, you do not need to derive it from scratch. However, if you lab requires a customized equation which you found using the laws of physics, you need to derive this equation in your report. Pretend you are writing for someone who has a similar level of physics knowledge as you do, but who otherwise knows nothing about your lab.
(4) You must analyze your data and convince me why your conclusions are correct, remembering that in science we convince with data and data analysis rather than emotion.
Part of this involves being quantitative rather than qualitative in your analysis, which I will describe in more detail in the quantitativeness section. But any good scientist knows she should approach her research as if she were trying to prove the opposite of what she the thinks is true. Such skepticism will lead to an iron-clad argument in your analysis, since you will have already considered any counterarguments. Back up everything you say with hard evidence.
(5) You must clearly state in your predictions what it is you are trying to prove, and then clearly state in your conclusion whether or not your predictions were verified, falsified, or neither.
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