5 Work

Learning Goals:

1. Identify assumptions and their effect on the outcome.
2. Use your physics knowledge to construct a measurement.
3. Write a scientific report.

Experiment

Use a length of string to attach an object to the IOLab. Hang the object over the edge of the table as shown while holding the IOLab in place with the wheels down. Release the IOLab and allow it to roll at least 30 cm while the block falls.

Using the above setup, invent a couple of ways to determine the work done by the string on the IOLab during the first 30 cm of its motion. Measure the work using two different methods and compare your results. Your report should include a clear description of your methods, your data, and you results with uncertainty. When you compare results, make sure to discuss reasons why the results might or might not be the same. Recall that a t-test is a good way to compare results that have uncertainties. If you need a refresher on how to do one, see this video: t-test.

Identifying Assumptions

• What to do: Try to identify the most important assumptions being made in the design of your measurement (see rubric).
• What to write: Describe the assumptions and how they may affect your experiment when you explain how your measurement procedure works.

Designing an Experiment

• What to do: Use physics concepts and equations to design the measurement procedure you will use.
• What to write: Use those equations and concepts to explain how your measurement procedure works.

Writing a Scientific Report

• What to do: Make sure you are using uncertainty in your reasoning and connecting your data with the real world.
• What to write: Report your measurement with uncertainty. Go through the significant elements listed in the rubric and make sure that you have included them in your report.

Grading Rubric:

(30 points): Identifying Assumptions and their effect on the outcome

The scientific report identifies assumptions made in the measurement and interpretation of the data. An effort is made to understand how invalid assumptions can affect the outcome of the experiment.

In the report	Omitted (0 points)	Attempted (10 points)	Partial mastery (20 points)	Near mastery (30 points)
The reports treatment of assumptions and sources of experimental error	is omitted or sufficiently unclear that it cannot be identified.	identifies at least one assumption made in the measurement and interpretation of the data. The assumption may not be relevant or there is no description of the impact of this assumption on the result.	identifies at least one relevant assumption made in the measurement and interpretation of the data. There is no description of the impact of this assumption on the result or it has been evaluated incorrectly.	identifies most relevant assumptions made in the measurement and interpretation of the data. The effect of the assumptions on the outcome is clear and correct.

(30 points): Constructing a Measurement

The scientific report describes how the measurement procedure works using equations and concepts from physics.

In the report	Omitted (0 points)	Attempted (10 points)	Partial mastery (20 points)	Near mastery (30 points)
The explanation of the procedure used to measure the physical quantity	is omitted or sufficiently unclear that it cannot be identified.	describes how the measurement procedure works using equations and physics concepts. The description is incomplete, or the design does not measure the desired quantity.	describes how the measurement procedure works using equations and physics concepts. The description is mostly clear, and the design is close to measuring the desired quantity.	describes clearly and nearly completely how the measurement procedure works using equations and physics concepts. The design measures the desired quantity.

(40 points): Writing a Scientific Report

The clear writing and structure of the scientific report allow a peer to understand and replicate the investigation and reproduce its results. The following significant elements are clear:

• Description of experiment (including pictures and/or diagrams).
• Presentation of data and calculations (as needed).
• Concluding statement summarizing your findings.
• Readability, clear wording, good grammar, and overall effort.
• Includes some estimates of the uncertainty of the measurements

In the report	Omitted (0 points)	Attempted (20 points)	Good (30 points)	Near mastery (40 points)
The writing and structure of the report	are sufficiently unclear that it cannot be understood by a peer.	are clear enough that it can be at least partially understood by a peer. Significant missing or unclear elements hamper understanding and/or overall effort needs significant improvement.	are clear enough that it can be mostly understood by a peer. At most one significant element is omitted or unclear, and/or overall effort needs only slight improvement.	are clear enough that the investigation can be understood and replicated by a peer. Almost all of the important details are included and clear.

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