Purpose:
The overt purpose of this lab is to explore practical uses of 1-dimensional kinematics. Perhaps more importantly this lab is an opportunity for you to experience the process of defining and executing an experiment to measure a particular quantity. This lab will be evaulated on your ability to figure out a plausible means of completing the assigned task, making the measurements in a way which minimizes any inherent uncertainties, and presenting the results in a coherent and comprehensive manner.
Procedure:
Your task is to find a way (create a process or model) to measure the height (from the
ground) of some location to be determined. In the past we have used outside railings and indoor stairwells. Your equipment will
be limited to stopwatches, meter sticks, and a physics "rock". What I provide for your physics rock varies from year to year. Sometimes it's a ping pong ball, sometimes a wine cork, or perhaps a badminton birdie. Your model is a mathematical expression into which I can plug the drop time and receive the height.
COVID:
The primary changes to this lab for COVIDland are the need for you to work independently, a different 'rock' for you to use, and the need for you to find a personal unknown. This changes will be noted in the descriptions below as well as in the Jupyterlab notebook.
- 1) Decide within your group how you will determine the behavior of your 'rock' and come talk to me about your plans. Your plan should articulate what measurements you will make, how you will use those measurements, and how you are planning to minimize uncertainties in your result. I will also expect that you can articulate you conceptual model of the behavior of the 'rock' and how the data might prove you wrong. If your plan seems reasonable I will provide you with the equipment. Trading lab supplies to the building superintendent for a look at the blueprints will not be an approved plan! Remember, in keeping with the spirit of the problem, that you should be able to use your techniques to measure the height of an object which is difficult to run up and down. Take enough data to be sure that you can determine the standard deviation of each of your data points. As you do your experiment consider the uncertainties in the measurements you are proposing to make. Have you considered things like reaction times, angular uncertainties, and individual variation? How will you minimize these effects?
- COVID Adjustment: The images below are of the 'rocks' you might be asked to use. Classically we use the badminton birdie with some extra weight inside it. For COVID we will use a wadded up piece of paper to simulate the birdie. Use a standard sheet of printer paper that is LOOSELY wadded up to have a diameter of 8-12 cm. That's about the width of your hand.
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2) Once you have some data return to the lab and use your data to validate (or invalidate) your conceptual model. You may well decide that your initial ideas about how the "rock" behaves will need to be modified or improved. Plot your initial set of data in a notebook or by hand and look to see if things are making sense. Where would it be most helpful to gather additional data points to clarify the behavior of your rock.
The standard deviation of your data affects the range of possible solutions to your model and you should be clear at this point what that means. Remember that the "actual" data point could reasonably be anywhere within the + or - 1 standard deviation window.
Enter your data into your python notebook and and produce a reasonable scatterplot with appropriate labels. In your lab write up you will be asked to comment on both the variability of your data and any idiosyncrasies that your reader might notice.
- 3) Using tools from your python notebook fit a 3rd order polynomial to your data and plot it along with your data. Plot this model 'on top' of your data and extend it out to 2.5 seconds. It should be clear from this plot that your model accurately matches your data and is different than an ideal physics rock.
- 4) Get out there and make those real measurements of the unknown height. Please be careful not to damage your fellow students-- you may need their help some day! Where we go to make the ultimate test of your model will depend on weather and the current state of the college buildings. I have a number of options we can use but most involve leaving the physics lab so be dressed for walking from building to building.
- COVID Adjustments: When we are f2f we typically find a tall stairwell to measure as our unknown. During COVID I am asking you to find a place that is higher than any of your test points to measure. I DO NOT want you to actually measure the height with a tape measure - only use your 'rock' please. You will be asked to include an image of your test location in your lab report notebook. Because many of these locations are likely to be outdoors choose a day when there is little or no wind (that's a complicating factor). If you have access to a 3 story stairwell that will work well including the one at the west end of the Health Careers Building on campus. There is a very tall staircase on the west side of the Regal Cinemas at the Old Mill. The chairlift at Mt Bachelor is an option. Please be attentive to your surroundings and don't scare anyone as you drop your 'rock'. I don't want to have to bail you out of jail as a result of this experiment.
LAB DELIVERABLES:
- I) Describe your data collection method in some detail so it could be reproduced by other researchers. Explain whether <0,0> is a real data point for this experiment and where you focused your attention as you gathered the data. Present your raw data completely and clearly in a markdown cell before proceeding to plot the data.
- III) How does your data support (or not) the idea that the 'rock' reaches terminal velocity? What is that terminal velocity indicated by your data if it does?
- IV) Complete the challenge task for this lab which involves using your carefully calibrated 'rock' to determine the height of the unknown (probably the stair well at the west end of the Health Careers Center).
- Rock Drop Rubric
