# The World’s Most Annoying Negative Sign

TL;DR If you want a quick way to gauge whether or not students understand the concept of potential energy, you can ask them to explain the origin of The World’s Most Annoying Negative Sign. It is merely a consequence of the very definition of potential energy, which is almost never explained coherently. In all of […]

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# Matter & Interactions II, Weeks 13 and 14

I’m combining two weeks in this post. The first week, we dealt with magnetic forces. One thing that I have never thought much about is the fact that the quantity is effectively an electric field, but one that depends on velocity. When velocity is involved, reference frames are involved, and that of course means Einstein […]

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# Matter & Interactions II, Week 5

This week was all about calculating electric fields for continuous charge distributions. This is usually students’ first exposure to what they think of as “calculus-based” physics because they are explicitly setting up and doing integrals. There’s lots going on behind the scenes though. In calculus class, students are used to manipulating functions by taking their […]

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# Matter & Interactions II, Week 4

This week was entirely flipped in that class time was devoted to letting students do whatever they needed to do to practice with the material in chapters 13 and 14. Until now, no one has touched the WebAssign problem sets or much programming. In an administrative environment where “teaching” is defined as lecturing from a […]

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# Conceptual Understanding in Introductory Physics XXVII: Mass and Charge

This question is inspired by my recent ramblings on electric charge and by the elements of thought in the Paul/Elder critical thinking framework. (a) In first semester physics, you learned that mass is necessary to calculate the gravitational force shared by two interacting entities. What are the physical implications of mass always being positive? (b) […]

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# Matter & Interactions II, Week 2

This week was yet another partial week. Between weather and holidays, we’ve not yet had a full week of classes. Such is life I guess. This week, we looked atÂ the electric field of a static particle and the electric field of a fixed dipole on the dipole’s axis and on the perpendicular bisector of the […]

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# Matter & Interactions II, Week 1

This week was supposed to begin on Monday, but we lost both Monday and Tuesday to snow and icy roads so this week was effectively just a two day week. On Wednesday, I demonstrated Jupyter notebooks and informed the class that effective this semester, we’re moving away from Classic VPython. From this point on, we […]

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# Conceptual Understanding in Introductory Physics XXIV: Distance Variations of Fields and Forces

This question was inspired by chapters 13, 14, and 15 of Matter & Interactions and would, I think, make a good final exam question even in courses where M&I isn’t used. The story line in those chapters makes a wonderful progression through different charge distributions and their fields and interactions with other similar charge distributions. […]

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# Conceptual Understanding in Introductory Physics XXIII: A Question About Fields

This question came to me while I was planning for this semester’s introductory calculus-based e&m course (using Matter & Interactions of course). My overall desire and plan is to move away from the traditional number crunching type of problems, where all students really do is manipulate coordinate components of vectors or perhaps vector magnitudes, all […]

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# Conceptual Understanding in Introductory Physics XIX: Why is current not a vector?

This is a very quick post addressing a frequently asked conceptual question. Maybe it my heightened awareness, but I’ve also seen this question asked a lot on various physics Q&A sites lately. It’s a question that gets to the heart of how vectors are often defined, loosely and incorrectly, in introductory physics. Here’s the question. […]

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