Physics 112 Lab Reports
This semester you will be asked to do experiments to test some of the physical ideas we learn about in this course. You will turn in a lab report for each experiment (with a couple of exceptions). They will have the following format.
Name, Partners, Date, Title: At the top of each report you must put your name, the names of your partners (with last names), the date the experiment was performed, and a title for your experiment.
Introduction: Briefly state the goal of the experiment. For example, if you intend to measure the acceleration of gravity, then you only need to say “We are going to measure the acceleration of gravity by timing how long it takes for a ball to drop a measured distance.”
Theory: Starting with first principles, you derive an equation for the quantity you wish to determine in terms of quantities you measure directly. In addition, define the variables in your equation. So for our acceleration of gravity example, it would go something like this…
“We know from kinematics: . In our experiment, we drop the ball, so that the initial velocity () is zero. Also, we are calling the height where we drop the ball with positive pointing towards the ground. Thus . Solving for the acceleration,
where= the acceleration of gravity, = the height the ball falls, and = the time the ball takes to fall this distance.”
Experiment: In this section, describe how the data was taken. Include enough details so that someone unfamiliar with your experiment could reproduce it with just your report. You also must include enough to convince the reader that you did things correctly. ALL experimental sections must also include a diagram and all of your data.
Analysis: In this section you crunch your numbers to come up with your result. In our acceleration of gravity experiment, where you presumably did the experiment 10 times, you got 10 values for the height and 10 values for the time. For each () pair you calculate 10 values for the acceleration of gravity. From these 10 values for g, compute the average and standard deviation for the uncertainty in your measurement of g.
Discussion: Talk about your result. Does it agree with what you expect? If so, say so, and why. In the case of our g experiment, we could say…
“The accepted value of g is 9.8 m/s2. We measured it here to be 10.6 ± 1.1 m/s2. The accepted value falls within uncertainty limits of our measurement, meaning that we have agreement between the two.”
If your measured value does NOT agree with what you expect, you must discuss possible reasons why this occurred.
“The accepted value of g is 9.8 m/s2. We measured it here to be 9.4 ± 0.2 m/s2. The accepted value does not agree with our measurement. We speculate that air resistance may have played a role in our experiment. Without air resistance, we expect the acceleration to be 9.8 m/s2. Air resistance slows things down, making the effective acceleration downward less.”
Saying that the reason that you didn’t get what you expected is due to “human error” is not acceptable. If you made a mistake, go back and fix it. Please don’t turn in a report on data you know has flaws. Quite often there are real reasons why things didn’t work out the way you expected.
If you have no expected value to compare yours to, then just write about if your result seems reasonable. Usually you have enough experience with these physical quantities by now to determine that. If you are still uncertain, you can always compare your result to another group’s in your class.
Conclusion: Here you briefly sum up the results of your experiment. This should stand alone and only sum up (repeat) what has already been said. Nothing new should go into your conclusion.
“Our experiment determined that in our location the acceleration of gravity is 9.4 ± 0.2 m/s2, which does not agree with the accepted value (9.8 m/s2) because of the effects of air resistance.”