Author: John F. Lindner

  • On Mercury One Day Lasts Two Years

    John F. Lindner

    Mercury has the most noncircular or eccentric orbit of any nondwarf planet in the solar system. This eccentricity has trapped Mercury in a 3:2 spin-orbit resonance, where it rotates three times for every two revolutions. When nearest Sun at perihelion, Sun’s tidal forces are greatest, Mercury’s spin and orbit (or rotation and revolution) nearly match,…

  • Dynamo

    John F. Lindner

    Stationary electric charges generate radial electric fields, and electric fields push positive charges (and pull negative charges). Moving charges also generate circulating magnetic fields, and magnetic fields deflect moving charges perpendicular to both the fields and their motions. All of electromagnetism follows. In particular, spin a conducting disk in a perpendicular magnetic field, and connect its axle to its…

  • Falcon Heavy

    John F. Lindner

    I was supervising Jr IS, but as I circulated around the lab, I watched the clock. Everyone was working quietly. Just before launch, I snuck back to my office and closed the door. The SpaceX Falcon Heavy was surrounded by swirling clouds of condensation at Kennedy Space Center‘s historic Pad 39A. Amidst spectactors’ cheers and…

  • The Impossible Problem

    John F. Lindner

    In 1969, Hans Freudenthal posed a puzzle that Martin Gardner would later call “The Impossible Problem”. Below is a 2000 version due to Erich Friedman. I have secretly chosen two nonzero digits and have separately told their sum to Sam and their product to Pam, both of whom are honest and logical. Pam says, “I…

  • Electronic Kilogram

    John F. Lindner

    The kilogram is the only metric unit still defined by an artifact. The International Prototype Kilogram, IPK or “Le Grand K”, is a golf-ball-sized platinum-iridium cylinder in a vault outside Paris. This year I expect the General Conference on Weights and Measures to replace the IKP by an electronic realization that balances gravitational and electrical power.…

  • Taylor Bowl

    John F. Lindner

    On Wednesday, September 13, 1989, I met with newly elected Physics Club officers Tom Taczak ’91, Dennis Kuhl ’90, Doug Halverson ’91, and Karen McEwen ’90 in Westminister House. I wrote in my diary, “first phys club meeting w. officers goes well”. That year we invented Taylor Bowl, an annual bowling competition between the Physics and Math clubs, both…

  • Newton’s Can(n)on

    John F. Lindner

    One of my favorite illustrations is the cannon thought experiment from volume three of Isaac Newton‘s Principia Mathematica. Johannes Kepler argued that planets orbit elliptically with Sol at one focus. Galileo Galilei argued that terrestrial bodies fall parabolically in space and time. Living in the next generation and standing on their shoulders, Newton realized that…

  • Ein Stein

    John F. Lindner

    I’ve been fascinated by aperiodic tilings of the plane since Martin Gardner first wrote about them in Scientific American. In the 1960s, Robert Berger discovered a set of 20 426 prototiles or tile-types that can tile the plane but only with no translational periodicity — a wonderful mix of the expected and the surprising, a kind of…

  • Gossamer Flight

    John F. Lindner

    As a kid, I devoured the pages of Popular Science magazine and was fascinated by the quest for human-powered flight: Was a flying bicycle possible? In the mid 1970s, I read that aerospace engineer Paul MacCready had assembled a team to build a large, lightweight, human-powered aircraft that could be rapidly repaired and redesigned. In…

  • The Cupola

    John F. Lindner

    In the sky is a castle, built in free fall, brick-by-brick, where the sun rises and sets every ninety minutes. The castle derives its energy from sunlight and recycles its water. Sealed against a vacuum, its inhabitants float and glide through its passageways and gaze down at Earth through its expansive cupola. In an earlier…

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