Lab Skills for AP Physics

First, make sure you are paying attention to the scoresheet that will be used to score your lab report. Below is an explanation of each section

A. Format. In this section you are scored on the organization of your report. All of the subsequent letters (B-F, but NOT A) should be a labeled section with clear organization of the elements required below. Underline or otherwise emphasize the section headings, i.e. Introduction

B. Introduction. Describe the purpose of the lab (which may not be something you can do in one sentence) by explaining the goal of the lab and also how it connects to the “story” of physics that we are constructing. Talk about the current unit of study and possibly the previous units. List several things that can be gained from the lab, for instance: “In class we are studying ____, and ____is a common _____in everyday life. It is important to understand ____ in order to physically model situations where an object is _______. The lab was done to find the effect of _____ on _____, and determine a mathematical relationship between the two variables by graphing the data.”

C. Apparatus and Data. The apparatus sketch is a drawing YOU create of the major components in the experimental setup. You should connect the labels “Independent Variable”, “Dependent Variable” and “Controlled Variable” with the parts of your drawing that depict the objects that are represented by those terms. If you changed the mass of a system, then all parts of the system (for example a drawing of a sensor cart and a drawing of a stack of lab masses) should have arrows or other linkages connecting them to the words “Independent Variable – System Mass”. If the Dependent Variable was monitored by a computer, for example, you could draw an arrow or other linkage from your drawing of the cart to “Dependent Variable – acceleration (Sensor Cart and Graphical Analysis App)”. If you used a stopwatch, draw a stopwatch and label it appropriately. If you used a meter stick, do the same. Labeling every single object that didn’t change as “Controlled Variable” is usually not necessary (don’t give a list of objects that you didn’t change “same string, track, classroom, experimenters. . . ” ). Label Controlled Variables that might have messed up your experiment, for instance if mass was one of the dependent variables, but another mass HAD to remain the same because it would have varied the force exerted on the system, you should include and label only the object that didn’t change as a Controlled Variable, as in “Controlled Variable – net Force (hanging mass)”.

D. Raw Data. There should be a clearly-labeled (variables and units) data table with an adequate number of measurements. Usually at least 6 different values of your independent variable are expected. If time permits, you should repeat measurements at least three times (you should ask in class if this is needed). This means your data table would have 30 entries: 6 different values of independent variable; 6 values of the dependent variable each recorded three times for 18 total entries; 6 values of the average of each dependent variable value. The quality of your data is important. Don’t record a measurement like 5 cm if you can do better; if you are using a meter stick or ruler to measure a stationary object, you ought to be able to record 5.00 cm. You should also include an estimate of the uncertainty of your measurements. If you are unsure what to record, ask about it.

E. Evaluation of Data. In this section the goal is to show a linear scatter-plot graph of the data with a best-fit equation, if possible, and to present an interpretation of the physical significance of these three elements: the slope of the best-fit equation, the intercept of the best-fit equation, and the “area under the curve.” Physical significance means relating these things to some part of the system being studied, or to some characteristic of the system. Not all of these have physical significance every time; if something does not have meaning, you should can just say “no physical significance”). You are expected to process non-linear data to make it linear. Therefore this section requires an additional data table with the processed data. Every bit of data in this section should be labeled with the correct physics name and/or variable and the correct physics units.

F. Conclusion. The ultimate goal of a paradigm lab in this class is to describe a conceptual model for the behavior of a new system. There should be some new information that you learned in this lab. Discuss that at first. Next, you should be describing the conceptual model. The basis for the model is the mathematical relationships that the linearized/processed data reveals in its best-fit equation (Section E.). You should be generalizing that relationship beyond the lab itself, so looking for the model on the AP Equation Table is a good idea. Describe the proportionality displayed, show a generalized equation (variables only, no numbers), and write a description in your own words of what the proportionality means. The other two representations can be anything you think of, including sketch graphs, motion diagrams, free-body diagrams, pictures, examples of other systems that behave in the same way, etc. All drawings or sketches must be labeled and their relevance to the model made clear, but diagrams are an excellent way to show you understand the model. Finally, discuss how good your results are. The estimated uncertainty from part D. could be referenced, as well as the statistics from your best-fit, or your opinion of the accuracy of the best-fit from a visual inspection (looking at the graph and making your own judgement).