The Laboratory Experience

Including:

Introduction

Laboratory experiences are an important part of most science courses. Scientists and engineers are trained to keep records of their laboratory work in bound notebooks, so anyone considering a career in one of these fields should learn how to correctly keep such a notebook. Also, the College Board states that "Most college placement policies assume that students have had laboratory experience, and students should be prepared to show evidence of their laboratory work in case the college asks for it." For further infomration on the importance of labs in the AP Physics course, please read the appropriate section in the College Board's AP Physics Course Description (PDF download).

The Lab Notebook

Your laboratory notebook will be used to record experimental data throughout the school year. I'm using the word "notebook" loosely here: for this particular class this year, you won't be recording your labs in a bound notebook as you did in your chemistry class. In here, each week you'll be writing up each lab using pages from your Engineer's Computation Pad, and turning in each lab individually. In all other ways, you'll need to follow the instructions for the lab "notebook" given here.

Some comments on the general style of the notebook: you are attempting to keep an accurate record of the experimental work you perform in this class. The notebook will not contain a perfect lab report of your experiment -that's something entirely different--but rather a record of what you did, how you did it, and what your results were. Although the notebook may reflect your personal style somewhat, your records need to be formal, neat, and complete enough so that any reasonably knowledgable person familiar with the subject of your experiment -- another student, or the instructor of this course - can read the entries, understand exactly what you did, and if necessary, repeat your experiment.

You need to write in black or blue ink. Pencil is unacceptable in a lab notebook - the marks are easily smeared, and may accidentally be erased. Never remove pages from your notebook, and never erase anything! If you make a mistake, draw a line through the mistake or cross it out -you may wish to add a small note indicating why the information you crossed out is incorrect.

Most importantly, your notebook needs to be set up for the experiment the day before the experiment!!! Some teachers refer to this as the "PreLab." When you come into the laboratory to perform an experiment, it is presumed that you will have already read the lab procedure, understood the details of the experiment, and prepared your notebook with the following information, or at least spaces where you can record the following information. Do not simply cut-and-paste the procedure from the lab handout - write your own procedure using the lab handout as a guide. On the day of the experiment, I will be coming around to check that you have correctly prepared your lab notebook with entries for the following items:

Outline of a Notebook Entry

  1. Title of Experiment
    Make the title, and all of the headings for each section in your notebook, descriptive enough that the reader can find information quickly and easily.
  2. Date and Time of Record

  3. The Name(s) of Lab Partners

  4. Objective
    This should simply be an elaboration of the title, possible giving the method used to conduct the experiment. (1-2 sentences)
  5. Theory
    Briefly explain the concepts used in the experiment, and a mathematical statement of these concepts and their derivation, if possible. (1-3 sentences)
  6. Equipment List
    Be as descriptive as possible. List the name of each piece of equipment used, the manufacturer, the model, the serial number, and any other information that may be pertinent to performing the lab.
  7. Experiment Set-Up
    Include a labeled sketch of the equipment set-up, details of component assembly, circuit diagrams, etc. If the set-up is included in the lab handout, it's easy enough to copy this drawing into your lab notebook. If the set-up is unknown, or will need to be created in the lab, be sure to leave space for sketching your set-up in your notebook.
  8. Statement of Procedure
    Briefly state the procedure that will be followed in conducting the experiment, either in a paragraph or two or as a numbered list stating the procedure step-by-step. Don't be excessively specific, but don't leave out any important information either. You may copy the lab handout procedure if it's available (or modify it as you see fit). If you need to develop your own procedure during the lab (as we'll sometimes do), be sure to leave enough space.
  9. Table of Observed Data
    These tables, like everything else in the notebook, should be constructed before you perform the lab. Tables for recording observed data should be clearly labeled with descriptive terms and units, logically organized, with plenty of room in the margins for corrections or notes.

    The day of your lab, data will be entered directly into the table, in blue or black ink, as the experiment is performed. Incorrect data should be neatly lined out, with an explanation of why the data has been lined out written somewhere nearby. The correct data should be written in the table, if possible. If a large number of mistakes have been made, or an entire data table even is found to be incorrect, neatly draw a large "X" over the table, then write a note in the margin explaining the error and referring them to the end of the experiment entry. You can draw a new data table there for entering the correct information.

    Often, we'll be using computers to observe and record data collected in the lab. For these labs only, you may cut out the personalized computer printouts collected in the lab, and use "Scotch"-style adhesive tape to include them in your lab notebook.
  10. Table of Calculated Results (and Sample Calculations)
    Any calculations necessary to yield final results should be neatly summarised in a Calculations Table. Clearly label all results, and be sure to include units. It isn't necessary to show your work for every single calculation performed, but you must include a) all formulae (i.e., F = ma) used to calculate results, and b) samples of each different type of calculation performed (i.e., 120 N = 40.0 kg x 3.00 m/s2 ). Showing these details will help the reader to understand your procedure, provide the instructor with evidence that you know what you're doing, and save you time if you need to perform this same type of calculation later on.
  11. Graph(s) of Results
    Where appropriate (nearly always), plot the data from your Calculations Tables on a graph. A brief review of graphs: All graphs must have a descriptive title, X and Y axes labeled with quantity and units. Adjust the scale of your graph so that the information being presented fills an entire page of your notebook. Data points, if plotted by hand, should be plotted with very small "pinprick" of ink, surrounded by a small, more visible, circle. When appropriate (nearly always) you should attempt to draw a smooth "best fit" line connecting the points. If you are graphing several sets of data on the same graph, clearly identify the different sets of data by using different shapes around the data points (circles, squares, triangles, etc), and include a key to these symbols.

    Instead of plotting by hand, you may wish to use some form of graphing software or spreadsheet program to create your graph. These printed graphs should conform to all the requirements listed above, and be neatly trimmed and taped into your lab notebook.
  12. Discussion
    The Discussion section of each entry is used to summarize your findings in paragraph form. Typically, the Discussion section will include:
    • Comparison with Known Values and Error Analysis
      Compare your results with known values -- how close are your findings to accepted values? Any time that your results have been obtained by more than a single method, or a standard value is available for your result, you must calculate the "percent difference" (in the case of results obtained by two different methods) or "percent error" (in the case of a result compared to a known quantity).

      To calculate the percent difference between two measured results, use the formula:

      To calculate the percent error between a measured result and a known value, use the formula:

    • Sources of Experimental Error
      [Thanks to E. Santochi and K. Hatch-Harrison for much of this section]

      "Experimental error" refers to variability in results due to limitations in the experimental design; it's the reason scientists perform multiple trials of any given experiment, and report their results as a statistal average with a plus or minus deviation included. (In this course, although we will often average measurements, we'll rarely do more advanced statistical analysis). In the "Sources of Experimental Error" section of the report, do list any observed reasons that you feel may have contributed to errors in your experiment, including specific problems with the equipment, difficulties in reading the equipment, or limitations in the design of the experiment. Don't just guess about why your experiment might have gone wrong -- only mention specific sources of error that you have a legitimate reason to believe affected your results, and explain how those sources of error affected your results, e.g. "The average final velocity of the pendulum was 15.6% smaller than it was at the top, which we presume is at least partly caused by loss of energy due to air friction as the pendulum swung down."

      Please don't refer to "human error." Examples of so-called human error include misreading a ruler, adding the wrong reagent to a reaction mixture, mistiming the reaction, miscalculations, or any kind of mistake. Scientists would never report the results of an experiment affected by human error--instead, they repeat the experiment more carefully.

      Points will be deducted from your lab report if you discuss "human error" instead of "experimental error."
    • Questions and Answers
      Restate any questions posed in the lab handout that you haven't already answered in the course of your entry, and provide answers in complete sentences.
  13. Summary of Results
    This is a brief, one-paragraph, summary of the results of this experiment, with a discussion of whether or not you think the experiment supports your hypothesis, or the subject material covered in class. Please note that science is unable to "prove" anything, so an experiment that measures forces, masses, and accelerations will never "prove" Newton's Second Law. We often try to "confirm" our physical descriptions of the world, however: your measurements might (and should!) confirm the validity of Newton's Second Law.

    Please note that although the instructor hopes you enjoyed--or at least appreciated--the lab experience, it's not appropriate to include any remarks on how you felt about the assignment, nor whether or not you liked it!

An Example of a Lab Entry

You might find it instructive to see an actual example of a lab entry completed by a student. This particular entry was a 5-page report on "Galileo's Ramps," and while there are minor errors in the report (you'll see occasional notations by the instructor), it's an excellent example of the kind of "look-feel" that is expected in a lab entry.

Use of the Lab Time

Before the Lab Period
Complete the lab entry up to the Table of Observed Data. Make sure that you've looked over the lab and have a good idea of what you're going to be doing during the 60-minutes of lab.

During the Lab Period
Most of the labs are designed for most people to complete within the 60-minute time period. Students who haven't prepared adequately, or who perform the experiment poorly the first time, may find that they'll need an additional 10-15 minutes to complete the work. If you manage to finish the lab and clean-up before the end of the lab period, you are expected to stay in the classroom to begin working on the remaining sections of their lab entry. All students need to get my dated signature on the lab to receive credit for their work.

After the Lab Period
Students will need to complete the remaining sections of the lab entry before turning in their completed lab on the Wednesday following the lab.

It is expected that you will collaborate with lab partners and other students in the class--you are encouraged to discuss the lab, and even to consult with others as you complete the lab entry. However, each students is expected to complete his or her own lab entry, with all calculations and written entries completed in his or her own words.

The Lab Manual

There's no pre-published lab manual for this course. Copies of the lab description for each week will be made available in class several days before the lab section, so you'll have plenty of time to prepare your notebook. Lab descriptions will also be made available on the website.

Grading Rubric for Lab Notebook

Lab Notebook entries will be worth varying amounts of points, depending on the difficulty of the experiment involved. The amount of points earned by a student on each entry or report will be determined according to the following rubric:

  • 100%
    The student demonstrates an excellent understanding of the laboratory exercise. All parts of the lab notebook entry or the lab report are clearly labeled and in the correct order. The equipment and experimental procedures used are clearly identified and explained. The data and results tables clearly show correct data, calculations processes, and results. Graphs are appropriately and correctly drawn. The discussion is clear, displays logical reasoning, and correctly identifies and explains potential sources of error. Minor errors in the entry or report, if present, do not detract from overall understanding. Communication is clear and effective. The notebook is turned in on time.
  • 80%
    The student demonstrates a solid understanding of the laboratory exercise. All parts of the lab notebook entry or the lab report are clearly labeled and in the correct order. The equipment and experimental procedures used are identified and explained. The data and results tables show data, calculations processes, and results. Graphs are appropriately and correctly drawn. The discussion is clear, displays logical reasoning, and identifies and explains potential sources of error. Minor errors in the entry or report may be present. Communication is mostly clear and effective.
  • 60%
    The student demonstrates a basic understanding of the laboratory exercise. The student has included most of the parts of the lab notebook entry or the lab report. The data and results tables show data, calculations processes, and results. Graphs are appropriately and correctly drawn. Major errors may be present. Writing may hinder effective communication.
  • 40%
    The student demonstrates a limited understanding of the laboratory exercise. The student has included some of the parts of the lab notebook entry or the lab report. Major errors and misconceptions are present. Writing may hinder effective communication.
  • 20%
    The student demonstrates minimal understanding of the laboratory exercise. The student has included few of the parts of the lab notebook entry or the lab report. The data and results tables show data, calculations processes, and results. Major errors are present. Writing may hinder effective communication.

List of Labs for the 2005-2006 School Year

This is a tentative, and incomplete, list of labs and activities that will be performed by AP Physics C students this school year. For more specific information on labs, see the Current Unit Course Materials or the Course Calendar.

First Semester

  • Acceleration of a Cart (Computer-based data collection)
  • Catch the Ball
  • Newton's Second Law of Motion
  • Centripetal Force of a Pendulum
  • Conservation of Energy in a Pendulum
  • Collision and Impulse (Air Track w/Photogates)
  • Ballistic Pendulum
  • Physics of Amusement Parks

Second Semester

  • Millikan's Oil Drop Experiment
  • Ohm's Law
  • RC Circuits
  • Electron Interaction with a Magnetic Field
  • Building an Electric Motor