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 graded 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 the railing of a landing behind the library. Your equipment will
be limited to stopwatches, meter sticks, and a physics "rock".
- 1) Decide within your group how you will perform your experiment and
come talk to me about your plans.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.
2) Once you have some data return to the lab and use your data to validate (or invalidate) initial model. You may well decide that your initial ideas about how the "rock" behaves will need to be modified or improved. I am not worried about how "good" your model is but rather how clearly you understand it and can support it with your data. 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. Consider the average behavior of your model as well as the best and worst cases. Remember that the "actual" data point could reasonably be anywhere within the + or - 1 standard deviation window.
- 3) Test your technique against an object whose
height you know. Actually take the time to do the calculation. Modify
your model as needed based on the feedback from this early calibration test.
It is my expectation that you will plot your actual data from your various tests as well as kinematic quantities that can be derived from your data in order to perform and thoughtful evaluation of your methodology.
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- 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! 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?
LAB DELIVERABLES:
- I) Present your data along with clear and complete plots (if appropriate) of your original data and both the velocity and the acceleration (or other relevant parameter) that you can derive from the data. Do this by hand rather than Maple since we will explore using Maple for these purposes next week. Be sure to determine and present the standard deviation of your data points.
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- II) Clearly state the mathematical or graphical model
you used to describe the rock's behavior as it falls through the air. Describe
how you validated your model using the heights of a known objects and your plots of the various kinematic variables. Clearly articulate all assumptions that you needed to make in this process. Discuss how the standard deviation of your data affects the range of possible solutions by determining a worst and best case version of your model.
- III) Complete the skills validation for this lab which involves using your carefully calibrated rock to determine the height of stair railing on the back of Modoc.
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- IV) For a significantly higher drop where you can still clearly see the rock land consider whether it would be more effective to use the physics "rock" from lab or a real rock of a similar size. Explain your reasoning from your data and experiences in this lab.
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- Rock Drop Rubric:
