Calibrated Peer Review – Creating an Assignment

I’ve been using calibrated peer review for several weeks now and I’m really enjoying it.  The assignments take a while to write, but the results are impressive.  I’ve been blown away by the quality of the students’ writings and they seem to be having fun with them.  I’m currently writing a new assignment and thought I’d walk you through it to give an idea about what is involved in using CPR.  Hopefully this will spark your interest and give you ideas on how to use it in your classroom.

1. Authoring an Assignment

When you first create a new assignment you are confronted with a screen showing all the steps you need to do.

After giving the assignment a title, in this case it’s The Story of Physics – Chapter 9 – Momentum, I go to Writing Prompt to write the heart of the assignment.  For this assignment the students must:

Write a short story that summarizes the important concepts from chapter 9, focusing primarily on topics related to linear momentum (i.e. don’t worry about angular momentum). Your story must cover the following topics:
1) Give the equation for momentum and describe it so that someone without a background in physics could understand.
2) Describe impulse to a non-physics person.
3) Explain how impulse and momentum are related.
4) Talk about what a system is, and how it is used in this chapter.
5) Give an example of a collision between a less massive and more massive object, discussing the momentum of the parts of the system, the system as a whole, and how momentum is transferred.
6) Give an example where a fragile object collides with something and comes to a stop. Consider one case where the object breaks and another case where it doesn’t break. In both cases the object should have the same initial velocity and come to a stop. Examples include catching a balloon or catching an egg, a person in a car crash, a glass hitting the floor, or anything else you can come up with.

One drawback to the CPR website is that all text must be entered in raw HTML.  For the most part this means starting all paragraphs with <p> and ending them with </p>, but it can be distracting.  On the plus side it means students can embed images and equations if they have familiarity with HTML.

I next move to the guiding questions.  These are a series of questions to help the students get started and give them a bit more guidance.  Here are the questions I wrote for this assignment:

How is Newton’s second law related to the impulse-momentum theory?

What does Newton’s third law have to do with momentum conservation?

What is a conservation law? (i.e. what does it mean for a physical quantity to be conserved?) Give an example.

What is the difference between an internal force and an external force and what affect does each of these have on the total momentum of a system?

What is the impulse approximation and why is it a valid approximation?

The next step for me is to write the student instructions.  If you look at the screen shot above you’ll notice I’m going through the list in reverse order, but I find this works for me.  Also, the student instructions, guiding questions, and writing prompt repeat quite a bit of information, but since students frequently skim through instructions or miss things it helps to reiterate what they need to do.  The instructions for this assignment are:

Try to remember a story you read as a child. Can you remember any of the names of the characters, what they did, how the story ended? Now try and remember the physics chapter you read a few days ago. Can you remember all the concepts introduced, the main points of the chapter?

Humans remember stories, we are drawn to stories. They draw us in and burn themselves into our brains. Stories make a topic more human. We are going to take advantage of this to develop a deeper understanding of physics. By wrapping the concepts in a narrative they will become more meaningful and easier to relate to.

The goal of this assignment is to write a short story about the physics concepts in chapter 9. Read chapter 9 and check out the online resources before you start writing. Your short story should be written at a level understandable by someone with no physics background. You will need to explain the concepts of momentum and impulse and how the two are related. Also, relate Newton’s second and third law to momentum and momentum conservation (see the online resources for help with this). Include a description of two collisions, one where a fragile object is stopped without breaking and one where it is stopped but breaks. Describe the difference between the two collisions. You must cover all the topics in the Writing Prompt and answer all the questions listed below.

Now I add links to any online resources.  Since I have my students focusing on summarizing material from the text I don’t give them many online resources, but in an earlier assignment covering forces, I had them research common misconceptions people have about forces and Newton’s laws.

I’m ready to create the assessment for the assignment.  This consists of a series of fairly straight-forward questions the students can use to assess the assignments.  I prefer yes-or-no type questions that are require as little subjectivity as possible.  My current strategy is simply to have the students check off if the assignment they are reviewing has completed the minimum requirements, but in the future I might focus more on whether the physics concepts are correctly depicted.  I’m still figuring things out.  Here is my list of questions for this assignment.

1. Does the story describe what momentum is? Content
2. Could someone without a physics background understand the description of momentum in the story? Content
3. Does the story describe what impulse is? Content
4. Could someone without a physics background understand the description of impulse in the story? Content
5. Does the story state that impulse is the same as (or equal to) the change in momentum of a system? Content
6. Does the story state something about internal forces being forces between objects within the system? Content
7. Does the story state something to the effect of an external force being a force on the system caused by something outside the system? Content
8. Does the story say that internal forces do not change the total momentum of the system? Content
9. Does the story indicate that external forces do change the total momentum of the system? Content
10. Does the story indicate that the impulse-momentum theorem is either another way of writing Newton’s second law or that the impulse-momentum theorem is a direct result or can be calculated from Newton’s second law? Content
11. Does the story indicate somehow that momentum conservation is a direct result of Newton’s third law? Content
12. Does the story give an example of a collision between a heavy object and a lighter object? Content
13. Does the story give an example with two cases, one where the object breaks and one where the object does not break? Content
14. Does the story state that you can reduce the force of a collision by extending the time of the collision?

There are two different categories of questions, content-related and style-related.  I don’t tend to worry about style but it is an option.

The final step is to write three calibration stories or answers.  I take my list of questions and try to write a story that satisfies almost all the questions.  I like to leave out one or two things, just so students can’t assume everything is answered.  For my mid-level quality and low-level quality answers I edit my original story, taking out some stuff.

Once I’ve written the calibration stories I’m done.  It is quite a long process, but I figure the time it will save me in grading more than makes up for it.  I plan on reusing these assignments for a while so I think it is a good investment of my time.

In my next post I’ll talk about things from the student perspective, and how grades are calculated.

How is Newton’s second law related to the impulse-momentum theory?What does Newton’s third law have to do with momentum conservation?

What is a conservation law? (i.e. what does it mean for a physical quantity to be conserved?) Give an example.

What is the difference between an internal force and an external force and what affect does each of these have on the total momentum of a system?

What is the impulse approximation and why is it a valid approximation?

Advertisements
This entry was posted in Teaching Physics and tagged . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s