Bare wires

In the last couple of years, I have made good use of the “bare wire” lab for electric potential difference. I first learned a version of this lab in the Modeling curriculum for electricity and magnetism. In this activity, students measure the potential difference of bare wires connected to a battery pack, but not connected to anything else. Lab2_Quiz_Quest1

This is extremely helpful in developing the idea that a wire can have zero potential difference along its length. And in developing the idea of potential difference being a difference between two different points.

Then, students connect a long bulb and a round bulb to the battery and repeat their measurements.


Finally, they make a graph of potential versus position.

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SBG Homework only?

Tell me this is stupid.

I haven’t found the time to implement Standards-Based Grading in my classes, even though I went to a great session on it at AAPT Summer Meeting in Portland in 2013.

So, over the break I devised this system for homework:

Objectives-Based Homework.

Your goal is no longer to score points. Your goal is now to demonstrate understanding. Each night’s homework will have one or more objectives. The standard objectives will be as follows:

-HW Objective 1. I followed the physics problem-solving process in constructing a solution to the problems (not exercises) or I wrote a clear, logical answer to the questions in the assignment.
-HW Objective 2. I understand and can restate the major concepts/big ideas inherent in the assignment.
-HW Objective 3. I can clearly identify any of the concepts, ideas, or mathematical applications in the assignment that I did not fully understand.
-HW Objective 4. I successfully solved/answered most of the problems/questions in the assignment.
-HW Objective 5. I can solve a new problem using the same concepts/ideas that were inherent in the assignment.

Homework will be assigned using textbook and online sources. There will be homework quizzes for some assignments. These will likely consist of one or more problems/questions that are similar to the problems/questions on the assignment (HW Objective 3). There may also be questions related to (HW Objective 2). This grade will be separate from the homework grade.

Individual homework assignments will be assessed in one of these three different ways:
– Students will complete a self-assessment, describing their success at meeting the objectives of the assignment.
– Students will submit a homework solution for a peer assessment. Assessment will primarily focus on whether the solution clearly demonstrates understanding of the problem-solving process.
– Students will submit a complete solution for instructor assessment or present their solution to the class. Assessment will primarily focus on whether the solution clearly demonstrates understanding of the problem-solving process.

Assessment of homework for process will be based on articles from The Physics Teacher by Kathleen Harper ( and Matthew Trawick (, and AIP by Sahana Murthy ( Rubrics I created from these articles are attached below.

I would assess on the basis of 2 – Clearly fulfills objective. 1 – Partially fulfills objective 0 – Did not complete or does not even partially fulfill objective.

Have to work a little more on how I’d translate this to grades, but generally I’m pretty generous on homework grades already. Major objection from students will likely come if I remove possibilities for extra credit on homework. Many of them earn a homework grade of greater than 100% under the current system, mostly by completing extra credit test review assignments on UTexas Quest (



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In the last few years, I have started the force unit off with demos, seat experiments, discussions, and conceptual questions. This year I decided to make a summary page for some of the activities we have done. They are first drafts, I can’t draw worth a darn, my handwriting is near illegible, and I unfortunately drew them on scrap paper with some dark images on the back. But, here they are. Not in any particular order.

This is an activity in which a cart with a dual-range force sensor (DFS) is wiggled back and forth in front of motion detector (MD) Students did this as a seat experiment in their groups.


Two strings stabilize a cart on a ramp. When the ramp is removed, the cart is stationary.

Incline Plane

Two blocks are suspended from pulleys with a spring scale inserted into the string. The students can’t see what the spring scale reads at first. This was presented as a puzzle, along with a ranking task of similar subject from this book

Tension Force

An optical lever magnifies the motion of the wall when a human presses on it. this was a whole-class demonstration.

Surface Force

A student jumps off of a force plate while it is collecting data. This was also a whole-class demo.

Force Plate

Several friction “seat experiments” are done with blocks, force sensors, and LabQuest 2s.


A HoverPuck (trade name “Kick Dis”) or a bowling ball is given a brief push and glides across the floor at a nearly constant velocity. This was a class activity, with a number of students participating.


A Newton’s 3rd Law demo with two force sensors and LabQuest2s was a final seat experiment.


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Modeling Terminology


In teaching modeling physics, there is some terminology that is used that I have found confusing.

For instance, we (modeling teachers and authors of “Teacher’s Notes” in the modeling materials) talk about the paradigms. The paradigm is a real thing that serves as a familiar example or exemplar of a concept. So, it’s pretty clear to say, when something moves with constant velocity, that it moves like the paradigm, the blinky buggy. As long as I explain what paradigm means, and repeat it a few times throughout the year, students seem pretty comfortable with this.

The problem arises with the term model. The modeling materials tend to talk about the “Constant Velocity Model”, a “math model” (an equation), a “graphical model” (a graph of the motion). Following this terminology, I suppose you could even say something about a verbal model (a description) and a pictorial model (a motion map).

I have always found all of these many models a bit confusing.

Last year, I decided to settle on a different terminology. There is the paradigm, the conceptual model for the paradigm, and the representations of the paradigm (mathematical, graphical, verbal, and pictorial). So, instead of saying equation or math model, I would refer to “mathematical representation.” Or instead of graph or graphical model, I say “graphical representation.” These are representations of the conceptual model.

So far, so good. Before, students seemed confused by talking about the Constant Velocity Model, the math model for constant velocity, and the graphical model for constant velocity. When I say representation, they haven’t hesitated, acted confused, or asked what I mean. And some have used the term themselves. I don’t remember many using the terms math model or graphical model so early in the year.

Perhaps old hat to everybody else, but it pleased me to figure this out.

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The Displacement Current

The Displacement Current is an important achievement in 19th century theoretical physics. James Clerk Maxwell applied the idea of induction to the area in between the capacitor plates in a charging (or discharging) circuit.  He found the changing flux acts like a current, a discovery that leads to later advances in both theory and technology.

Professor Lewin derives the displacement current term:

Here’s another, by Dr. Phys:

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Diff. Eq Review/Cheat Sheet for APPC

Please check it for errors, comments. It doesn’t show solutions for everything, just how to set stuff up. I have mixed feelings about posting this or giving it to students:

1. Likely it’s full of errors that some won’t catch.
2. They really ought to be doing this sort of thing themselves.
3. Some will try to memorize without understanding – a tactic of little value.

Anyway, here it is.
DiffEQN_CheatSht 001

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APlusPhysics – Maxwell’s Equations

Dan Fullerton on Maxwell’s equations, nice summary of what you need to know for AP Physics C E and M exam.

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