Matter & Interactions I, Week 4

This week we formally wrapped our coverage (I hate that word) of special relativity. My goal never has been for students to do complicated numerical problems. Instead, I wanted them to understand the foundations of special relativity with an emphasis on the invariance of light’s speed, the loss of absolute simultaneity, and loss of absolute […]

Matter & Interactions I, Week 3

This week, we encountered what, in my opinion, is the most fundamental aspect of special relativity: the loss of absolute simultaneity. The Michelson-Morley experiment established that light’s speed must be invariant. An immediate consequence of this is that two events that are simultaneous in one inertial frame cannot be simultaneous in any other frame. Last […]

Matter & Interactions I, Week 2

This week we began readings from chapter 36 (email me if you want a copy) of Arnold Arons’ 1965 calculus-based textbook Development of Concepts of Physics (rare, but occasionally found on the used market…I have two copies and I hope to get Dover to reissue the book in paperback). This is the chapter on special relativity, and in my […]

Conceptual Physics: Time in Special Relativity

This is basically a quick brain dump. I’m teaching a section of conceptual physics this semester for the first time in many years. It has caused me to revisit everything about the topics I’m including in the course. When the course was assigned to me, I immediately decided to make it consist of twentieth century […]

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 […]

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 […]

Building Up to Simultaneity (Activity)

Here’s a classroom activity intended to demonstrate the issue of simultaneity in measuring a stick’s length. Students need a calibrated metre stick (I’m trying to get into the habit of spelling it that way), another stick approximately 1/3 m long although the precise length is unimportant, two coins of the same denomination or two small pea-size balls […]

Conceptual Understanding in Introductory Physics IV: Can a person move at 0.99c?

I have tens of these questions ready to use here so this series will likely go on for a long time. Part of my strategy for posting each one separately is to get me into the habit of writing regular posts. While these first few are, or should be, relatively simple I promise the difficulty […]