Author: John F. Lindner

  • Anholonomy

    John F. Lindner

    A falling cat’s twisting returns its shape to normal but rotates its body to land feet down. Earth’s spin returns a Foucault pendulum to its initial position in one day but rotates its oscillation plane. Parallel parking cyclically rotates a car’s front wheels but shifts the car sideways. These are examples of nonholonomic motions or…

  • Norton’s Dome

    John F. Lindner

    Norton’s Dome is a fascinating counterexample in classical mechanics: A frictionless mass balanced at the dome’s top can remain there forever — but can also spontaneously slide down! The Shape Norton’s dome has a cubed square root profile: if the downward height is at dome arc length , then If max height when max arc length…

  • Moon Dance

    John F. Lindner

    I ran up the stairs to Studio Art. Justine was already rolling out the treadmill, so I climbed another flight of stairs to the old running track and let down both ends of the steel cable, one end connected to the harness and the other to the sandbag counterweight. Our reduced gravity rig was basically…

  • 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…

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