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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

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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

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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

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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

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Pseudowork and real work

I have a story to tell about pseudowork, the integral of a 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 as … Continue reading

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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

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A taste of geometric algebra

David Hestenes’ goal for geometric algebra is to subsume under one umbrella many different kinds of mathematics used by scientists and engineers (see the Hestenes web site, and especially his Oersted Medal Lecture). The key to this unification is to … Continue reading

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What is Light? What are Radio Waves?

A talk given at a Santa Fe Science Cafe, 2013 Jan. 16 Abstract of the talk Video of the talk Interview on KSFR radio (15 minutes; choose the 3rd audio option) The great discovery by Maxwell about 150 years ago … Continue reading

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Calculus and formal reasoning in intro physics

A physicist asked me, “One thing I noticed in most recent introductory physics textbooks is the slow disappearance of calculus (integrals and derivatives). Even calculus-based physics now hardly uses any calculus. What is the reason for that?” Here is what … Continue reading

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Quantum entanglement

A non-physicist friend expressed deep puzzlement about measurements at opposite ends of the Universe being somehow linked. Here I describe what I take to be the current state of theoretical and experimental knowledge about the “spooky action at a distance” … Continue reading

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