## A Flat Earth?

A 10-minute video summarizes this article: tinyurl.com/AFlatEarthModel A one-hour physics colloquium based on this article. 50-minuta versio tinyurl.com/PlataTero, kun partopreno de Derek Roff. In the US and in Britain there are organized groups of people who strongly believe that the … Continue reading

Posted in Uncategorized | 27 Comments

## Reciprocity of magnetic forces

Consider the following interaction between a proton and an electron: The electric forces between the proton and electron exhibit “reciprocity.” That is, the electric force that the proton exerts on the electron is equal in magnitude and opposite in direction … Continue reading

Posted in Uncategorized | 12 Comments

## What energy is used by a magnet to attract another magnet?

People sometimes ask, “What is the source of the energy expended by a magnet to attract another magnet, giving it kinetic energy? After all, the magnet doesn’t get colder.” The energy aspects of a magnet accelerating another magnet can indeed … Continue reading

Posted in Uncategorized | 7 Comments

## Magnetic forces do no (net) work

Because the magnetic force on a moving charge is perpendicular to the velocity, the work done by a magnetic force is zero. However, in a multiparticle system it can happen that magnetic forces can rearrange the energy within the system, … Continue reading

Posted in Uncategorized | 3 Comments

## EMF in a solenoid

A colleague identified a puzzle concerning Faraday’s law. A circular loop at the center of a long solenoid with time-varying magnetic field will run a current due to the emf, which is the path integral of the (curly) non-Coulomb electric … Continue reading

Posted in Uncategorized | 23 Comments

## A time line for VPython development

Here is a time line for the development of VPython, an extension to the Python programming language that makes it unusually easy to generate navigable real-time 3D animations (vpython.org). 1997: While at Carnegie Mellon, after writing a volume on introductory … Continue reading

Posted in Uncategorized | 11 Comments

## Pseudowork and real work

I have a story to tell about pseudowork, the integral of the net force along the displacement of the center of mass, which is different from the true work done by a force on a system, which must be calculated … Continue reading

Posted in Uncategorized | 41 Comments

## Feynman and transients

In 1966-1969 I was active in an experimental particle physics group at Caltech and taught intro physics using the Feynman Lectures on Physics as the textbook, which was a fantastic experience. I often saw Feynman at lunch in the Caltech … Continue reading