If you recall, during the first lab of the quarter we asked you to complete a pre-survey on your attitudes about experimental physics. Now that the course is ending, we are asking you to complete the corresponding post-survey which will look for changes.

The survey will not affect your grade. Instructors and TAs will never see your individual responses. Identifying information is collected only so the survey administrators can connect the pre- and post-survey responses.

Your TA will provide time for everyone to complete this survey before starting today's experiment.

The survey closes at midnight on Nov 18 and cannot be reopened.

E-CLASS for PHYS 141

In physics we frequently need to make simplifying assumptions in order to arrive at exact solutions to problems. In your physics lectures this quarter you have likely encountered simplifications such as “frictionless surfaces”, or “massless strings”. Physicists frequently joke about “spherical cows” and “massless elephants”.

Many introductory physics labs go to great lengths to try and minimize certain factors such as friction in a system. A common example are lab experiments designed to test conservation laws, such as conservation of energy. Often times such experiments are performed on an air track which allows specially designed carts to move on a column of air, thus greatly reducing energy losses due to frictional effects.

In research labs however, experimental physicists have to deal with real world systems where things like friction can no longer be simply swept under the rug so to speak. We have to learn how to identify and account for the non-ideal factors in our experiments. An experiment designed to make very precise measurements of the period of a pendulum will eventually have to account for factors such as air resistance and the rotation of the earth for example.

In this lab course we are training you to think like an experimental physicist, and todays lab will focus on conducting several straight forward experiments where the challenge is to figure out how to account for these sorts of non-ideal effects.

When a spring is held in a compressed state, energy is stored in the spring which can be used to do work on an object. The goal of this lab is to predict how far your iOLab device will travel across the lab bench when propelled by the energy stored in a compressed spring. To do this you will:

• Attach the spring bumper to the force sensor on your iOLab device.
• Set the iOLab on the lab bench, wheel side down, and push it up against a fixed object so that the spring is compressed by a known amount.
• Release the iOLab device such that the spring propels it in a straight line.
• Measure how far the device travels.
• Repeat to get a good average.

This is basically a conservation of energy problem for a system that experiences significant energy loss as it rolls. In principle the potential energy stored in the spring when it is compressed gets converted into kinetic energy in the motion of the iOLab device. Friction and irregularities in the surface of the lab bench will cause the device to lose energy as it travels, thus determining how far it goes. In order to make an accurate prediction, with appropriate uncertainties, you will need to determine the following:

• How much potential energy is stored in the spring as it is compressed. The physics concepts involved include Hooke's Law and Work. What physical parameters of the spring do you need to know and how can you measure them?

• How much energy is lost due to rolling friction and other effects as the device rolls across the lab bench?

You will find that the wheel and force sensors in the iOLab device are very useful for this lab. You will need to devise and conduct separate experiments to determine the energy stored in the spring (with uncertainties), and the rate of energy loss (again with uncertainties) so that you can calculate the expected length of travel of the device for a known amount of energy (with, you guessed it, uncertainties) stored in the spring.

After the lab is over, each student in your group will write up their own conclusions and submit them to their TA via Canvas. Your individual conclusions are due no later than 48 hours before the start of your next lab. Your conclusions will be graded for completeness and quality according to the rubric on the PHYS141 main wiki page.

Even though you worked as part of a group in the lab, and submitted one group notebook, your individual conclusions must be your own work.

Your conclusions should not require more than one or two pages of text, though the final document may be longer if you include plots of data. The focus of your writeup should be on the final conclusions which you are able to draw based on your work in the lab. Assume that the reader, i.e. your TA, knows what the lab is about and has access to your groups notebook. As such you do NOT need to write about the following:

• What you did in the lab.
• Background and motivation for the experiment.
• Theory.
• Details of apparatus used.

You are expected to clearly articulate your conclusions and discuss how your data support those conclusions.

Take a moment to think a bit about the learning objectives for this lab course. These were listed on the lab homepage, but as a reminder we provide them again here.

* These goals were first outlined by the Physics Education Research Lab at Cornell University for labs at all levels, but especially for introductory labs. You can read more about the philosophy behind these learning goals  here.)

Drawing scientifically appropriate and meaningful conclusions is not easy. It is a skill which is learned and which you develop over time. Here are some thoughts to guide you in drawing conclusions from your lab work.

The conclusion is your interpretation and discussion of your data.

• What do your data tell you?
• How do your data match the model (or models) you were comparing against, or to your expectations in general? (Sometimes this means using the $t^{\prime}$ test, but other times it means making qualitative comparisons.)
• Were you able to estimate uncertainties well, or do you see room to make changes or improvements in the technique?
• Do your results lead to new questions?
• At the end of the lab period were there things you learned about what you did and how you did it that you could use to improve your experiment and obtain more precise results?

In about a few paragraphs, draw conclusions from the pendulum data you collected today. Address both the qualitative and quantitative aspects of the experiment and feel free to use plots, tables or anything else from your notebook to support your words. Don't include throw-away statements like “Looks good” or “Agrees pretty well”; instead, try to be precise.

Remember… your goal is not to discover some “correct” answer. In fact, approaching any experiment with that mind set is the wrong thing to do. You must always strive to reach conclusions which are supported by your data, regardless of what you think the “right” answer should be. Never should you state a conclusion which is contradicted by the data. Stating that the results of your experiment are inconclusive, or do not agree with theoretical predictions is completely acceptable if that is what your data indicate. Trying to shoehorn your data into agree with some preconceived expectation when you cannot support that claim is actually considered to be fraudulent, don't do that.

In the next lab, we will return to the pendulum to take more measurements with the goal of increasing the precision of your measurements based on what you learned in this lab period. This is a common theme in experimental physics; making measurements, analyzing your data, gaining experience and learning how to improve your experimental technique, going back into the lab to refine your experiment and improve your results… We assure you that no one plans and executes an experiment all in one go.

You have now completed the lab component for PHYS141!

Enjoy your Thanksgiving break and good luck with final exams.

If you missed a lab during the quarter please be sure to reach out to your TA. There will be one makeup lab during 9th week. If you do not need to makeup a missed lab you do not have any lab assignment for 9th week!