# Proving the Absence of Length Contraction Perpendicular to Velocity

When teaching conceptual physics, students almost always ask why length contraction only occurs parallel to velocity and not perpendicular to it. That’s a meaty conceptual question and one that always leaves me looking for a convincing, non mathematical explanation. Earlier this semester, I finally found what I think is the best one I’ve ever heard […]

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# Matter & Interactions II, Week 7

This week, I was away at the winter AAPT meeting in Atlanta. Students began working on the experiments from chapter 17, which serve to introduce magnetic fields. I want to emphasize some really cool things about the mathematical expression for a particle’s magnetic field: This is really a single particle form of the Biot-Savart law. […]

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# Conceptual Understanding in Introductory Physics VI: Naming Reference Frames

In this post, I present a question from special relativity that addresses how we name reference frames. Students tend to blindly memorize names, terms, labels, and other minutiae that have little or nothing to do with the underlying physics. In one problem, a clock is stated to be in the S frame and has a […]

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# Conceptual Understanding in Introductory Physics V: Length Contraction and Time Dilation

This series continues with yet another question from introductory special relativity. I have seen this question asked many times in various places and unfortunately, have rarely seen the correct answer given. After studying special relativity, students sometimes ask, “What really happens to a moving rod to make it contract?” and “What really happens to a […]

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